Input: adp5589-keys - fix pull mask setting

The pull mask is created by looping each row (column) and building an
8-bit integer with the configuration. It is written byte-by-byte, when
we reach the end of the rows (columns) or we're at the 3rd line (which
finishes the first byte, since each pin is 2bits on the mask).

However, this only works if we have at most 8 pins (2 bytes), which is
not the case for the ADP5589. So, write the byte at each boundary (every
4 rows/columns).

Signed-off-by: Guido Martínez <guido@vanguardiasur.com.ar>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>