selftests: watchdog: Fix ioctl SET* error paths to take oneshot exit path

When ioctls for WDIOC_SETOPTIONS (WDIOS_DISABLECARD or WDIOS_ENABLECARD),
WDIOC_SETTIMEOUT, and WDIOC_SETPRETIMEOUT fail, the error path continues
to handler watchdog timer until user terminates it. When ioctl returns
error, it might not be safe to let the watchdog tick. The error could be
due an unsupported ioctl command or some other error.

Fix it to handle error paths as oneshot to stop the watchdog ticks and
exit right away.

Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>