Input: omap4-keypad - move rest of key scanning to a separate function

Let's move rest of the key scanning code to omap4_keypad_scan_keys().
We will use omap4_keypad_scan_keys() also for implementing errata
handling to clear the stuck last key in the following patch.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20210110190529.46135-4-tony@atomide.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>