kernel/mutex: prevent priority inheritance from lowering owner's prio
kernel/mutex: prevent priority inheritance from lowering owner's prio

If the system's priority inheritance priority ceiling is not the same as
the highest priority in the system, it was possible for a thread owning
the mutex to get its priority lowered instead of left unchanged.

Change-Id: Ic06a1c4a66322c2949b2ba2f53efa03200fb1fc1
Signed-off-by: Benjamin Walsh <2c289a12a296c7195a7f06fd0f3fe281728960bf@gmail.com>

zephyrproject-rtos/zephyr,runchip/zephyr-cc3220,punitvara/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,bigdinotech/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,erwango/zephyr,explora26/zephyr,tidyjiang8/zephyr-doc,galak/zephyr,tidyjiang8/zephyr-doc,aceofall/zephyr-iotos,mbolivar/zephyr,fbsder/zephyr,bboozzoo/zephyr,zephyrproject-rtos/zephyr,sharronliu/zephyr,aceofall/zephyr-iotos,holtmann/zephyr,nashif/zephyr,Vudentz/zephyr,mbolivar/zephyr,runchip/zephyr-cc3220,mbolivar/zephyr,sharronliu/zephyr,runchip/zephyr-cc3200,fbsder/zephyr,pklazy/zephyr,rsalveti/zephyr,zephyriot/zephyr,fractalclone/zephyr-riscv,kraj/zephyr,runchip/zephyr-cc3200,mbolivar/zephyr,bboozzoo/zephyr,punitvara/zephyr,aceofall/zephyr-iotos,holtmann/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,fbsder/zephyr,bigdinotech/zephyr,explora26/zephyr,kraj/zephyr,pklazy/zephyr,finikorg/zephyr,nashif/zephyr,erwango/zephyr,ldts/zephyr,mbolivar/zephyr,explora26/zephyr,zephyriot/zephyr,finikorg/zephyr,fractalclone/zephyr-riscv,zephyrproject-rtos/zephyr,punitvara/zephyr,ldts/zephyr,ldts/zephyr,tidyjiang8/zephyr-doc,aceofall/zephyr-iotos,bigdinotech/zephyr,GiulianoFranchetto/zephyr,bboozzoo/zephyr,fractalclone/zephyr-riscv,kraj/zephyr,Vudentz/zephyr,pklazy/zephyr,Vudentz/zephyr,kraj/zephyr,sharronliu/zephyr,zephyriot/zephyr,aceofall/zephyr-iotos,bboozzoo/zephyr,holtmann/zephyr,sharronliu/zephyr,erwango/zephyr,rsalveti/zephyr,runchip/zephyr-cc3200,zephyriot/zephyr,erwango/zephyr,bboozzoo/zephyr,rsalveti/zephyr,explora26/zephyr,zephyriot/zephyr,erwango/zephyr,fractalclone/zephyr-riscv,fbsder/zephyr,sharronliu/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,bigdinotech/zephyr,fractalclone/zephyr-riscv,galak/zephyr,runchip/zephyr-cc3200,zephyrproject-rtos/zephyr,nashif/zephyr,ldts/zephyr,rsalveti/zephyr,fbsder/zephyr,explora26/zephyr,tidyjiang8/zephyr-doc,punitvara/zephyr,GiulianoFranchetto/zephyr,tidyjiang8/zephyr-doc,kraj/zephyr,punitvara/zephyr,rsalveti/zephyr,runchip/zephyr-cc3220,finikorg/zephyr,runchip/zephyr-cc3220,GiulianoFranchetto/zephyr,bigdinotech/zephyr,galak/zephyr,Vudentz/zephyr,runchip/zephyr-cc3200,holtmann/zephyr,finikorg/zephyr,pklazy/zephyr,pklazy/zephyr,holtmann/zephyr