Input: pxa27x_keypad - fix NULL pointer dereference

A NULL pointer dereference exception occurs in the driver probe function when
device tree is used.  The pdata pointer will be NULL in this case, but the code
dereferences it in all cases.  When device tree is used, a platform data
structure is allocated and initialized, and in all cases this pointer is copied
to the driver's private data, so the variable being tested should be accessed
through the driver's private data structure.

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>