serial: imx: remove redundant USR2 read from FIFO reading loop

There is no need to read USR2 twice at every loop iteration: get rid of the
second read.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Link: https://lore.kernel.org/r/20230201142700.4346-6-sorganov@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>