Revert "serial: max310x: rework RX interrupt handling"

This reverts commit fce3c5c1.

FIFO is triggered 4 intervals after receiving a byte, it's good
when we don't care about the time of reception, but are only
interested in the presence of any activity on the line.
Unfortunately, this method is not suitable for all tasks,
for example, the RS-485 protocol will not work properly,
since the state machine must track the request-response time
and after the timeout expires, a decision is made that the device
on the line is not responding.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Link: https://lore.kernel.org/r/20210217080608.31192-1-shc_work@mail.ru


Fixes: fce3c5c1 ("serial: max310x: rework RX interrupt handling")
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>