drivers: i3c: mcux: tighten the FIFO read

At high i3c rates, the mcux_i3c_do_one_xfer_read()
could get into an infinite loop where the rx_count
kept returning 0 but the complete status bit
was never set. I believe the problem was that
the function was not emptying the FIFO fast enough,
so tighten the loop that processes the FIFO.

Signed-off-by: Mike J. Chen <mjchen@google.com>