lib: os: add braces to 'if' statements
lib: os: add braces to 'if' statements

An 'if' (expression) construct shall be followed by a compound
statement.
Add braces to improve readability and maintainability.

Found as a coding guideline violation (MISRA R15.6) by static
coding scanning tool.

Signed-off-by: Maksim Masalski <00762c94550ce68b2a0e3f1373f5a19cd4f4bbbb@intel.com>

galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr