Input: omap-keypad - clear interrupts on open

According to TRM, the recommended way for keyboard controller
initialization is clear the interrupt-status register, then set up
certain keyboard events for generating an interrupt request and
set up expected source of wake-up event that generates a wake-up
request.

Signed-off-by: Illia Smyrnov <illia.smyrnov@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>