Staging: android: timed_gpio: Properly discard invalid timeout values.

The timed output device never previously checked the return value of sscanf,
resulting in an uninitialized int being passed to enable() if input value
was invalid.

Signed-off-by: Mike Lockwood <lockwood@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>