kernel: sched.c: Fix datatype mismatch in comparision
kernel: sched.c: Fix datatype mismatch in comparision

All arguments comes from userspace has data type u32_t but
base.prio has data type of s8_t. Comparision between s8_t and u32_t
cannot be done. That's why typecast priority coming from userspace(prio)
to s8_t data type.

Signed-off-by: Punit Vara <2ba5e82aa6fb4e68460f49bedefe3af5717cea9b@intel.com>

finikorg/zephyr,galak/zephyr,aceofall/zephyr-iotos,mbolivar/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,galak/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,kraj/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,kraj/zephyr,zephyriot/zephyr,zephyriot/zephyr,explora26/zephyr,nashif/zephyr,galak/zephyr,ldts/zephyr,Vudentz/zephyr,nashif/zephyr,aceofall/zephyr-iotos,finikorg/zephyr,finikorg/zephyr,explora26/zephyr,explora26/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,zephyriot/zephyr,kraj/zephyr,ldts/zephyr,zephyriot/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,explora26/zephyr,ldts/zephyr,mbolivar/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,Vudentz/zephyr,Vudentz/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,punitvara/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,ldts/zephyr,explora26/zephyr,punitvara/zephyr,galak/zephyr,aceofall/zephyr-iotos