Input: pxa27x-keypad - fix generating scancode

The number of columns of pxa27x-keypad used by various boards is not fixed.
When building keymap with call to:

matrix_keypad_build_keymap(keymap_data, NULL,
                           pdata->matrix_key_rows,
                           pdata->matrix_key_cols,
                           keypad->keycodes, input_dev);

it will internally calculate needed row shift and use it to fill the
keymap. Therefore when calculating the "scancode" we should no longer use
constant row shift but also calculate it from number of columns.

Signed-off-by: Chao Xie <chao.xie@marvell.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>