input: gpio-matrix-keypad: Accept device name from device node

The device name is not properly set if the platform device
is created from device tree.  Read "input-name" property to
set the device name.

Change-Id: Ib348df17f2222d88032435424cfcff9d37054ddd
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>
Signed-off-by: Chetan C R <cchinnad@codeaurora.org>