drivers: wdt: sam0:  fix register access in feed()
drivers: wdt: sam0:  fix register access in feed()

The wdt CLEAR register is a write synchronized register.
To avoid bus stall, check the status of SYNCBUSY before
accessing the register.

Use SYNCBUSY register for SAM E.
If the wdt is syncing, return -EAGAIN to avoid bus stall.

Signed-off-by: Steven Slupsky <3dc7ae64181eb0aabccfd4b5e04f43aed07e50e1@gmail.com>

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