Input: omap-keypad - fix build warning

Fix the following build warning:

drivers/input/keyboard/omap-keypad.c: In function 'omap_kp_probe':
drivers/input/keyboard/omap-keypad.c:418: warning: 'row_idx' is used uninitialized in this function
drivers/input/keyboard/omap-keypad.c:421: warning: 'col_idx' is used uninitialized in this function

These variables are useful when cpu_is_omap24xx(), and otherwise just
for useless cleanup.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>