Input: pixcir_i2c_ts - fix receive error

The i2c_master_recv() uses readsize to receive data from i2c but compares
to size of rdbuf which is always 27. This would cause problem when the
max_fingers is not 5. Change the comparison value to readsize instead.

Fixes: 36874c7e

 ("Input: pixcir_i2c_ts - support up to 5 fingers and
hardware tracking IDs:)

Cc: stable@vger.kernel.org
Signed-off-by: Frodo Lai <frodo_lai@bcmcom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>