serial: imx: do not break from FIFO reading loop prematurely

There is no reason to prematurely break out of FIFO reading loop, and it
might cause needless reenters into ISR, so keep reading until FIFO is
empty.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Link: https://lore.kernel.org/r/20230201142700.4346-5-sorganov@gmail.com


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