After further testing periods of ~16 ms have been observed
between interrupts indicating that there is receive data in
the FIFO.  To accomodate that, increase the time the driver
waits before deciding there is no more data to receive to
20 ms.  The macro that represents that delay is
'TRF7970A_WAIT_FOR_RX_DATA_TIMEOUT'.
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>