Documentation: Fix typo in watchdog-kernel-api.txt

Correct spelling "retruns" to "returns" in
Documentations/watchdog/watchdog-kernel-api.txt

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
1 file changed