Commit da1f026b ("Keyboard: omap-keypad:
use matrix_keypad.h") switched the driver to use matrix keypad
infrastructure, which made array of keycodes to be unsigned short, and
caused the test for negativity never trigger. This leads to the following
static checker warning:

	drivers/input/keyboard/omap-keypad.c:158 omap_kp_tasklet()
	warn: 'keycodes[]' is never negative.

Given that we did not care about this check for a few years already let's
simply remove it.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>