arch: arm: typos and style fixes in userspace.S
arch: arm: typos and style fixes in userspace.S

Some minor typo fixes in inline comments within
arch/arm/core/userspace.S.

Signed-off-by: Ioannis Glaropoulos <5921cc8bab7e1d4329f52fd8f6268f9692e3de80@nordicsemi.no>

punitvara/zephyr,ldts/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,explora26/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,ldts/zephyr,Vudentz/zephyr,finikorg/zephyr,punitvara/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,nashif/zephyr,ldts/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,explora26/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,explora26/zephyr,ldts/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,galak/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,GiulianoFranchetto/zephyr