Input: omap-keypad - remove adjusting of scan delay

As of 35f8679f

 ("Input: omap-keypad -
remove dead check") we no longer declare keypresses as spurious, therefore
we can use constant delay between scans.

Suggested-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>