kernel: work_q: use flags_get() in work_delayable_busy_get_locked().
kernel: work_q: use flags_get() in work_delayable_busy_get_locked().

The k_work::flags field is not an atomic_t and would cause
-Wpointer-sign warning on some compilers. This function was the only
one in work.c to use atomic_get() so there is no benefit to atomicity.

Signed-off-by: Chris Reed <5c8e7a799cb891a0ec7887f2dd5d3bfb138b5f9c@arm.com>

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