drivers: mspi_dw: Add error reporting on RX FIFO overflow

Immediately finish an RX transfer when the RX FIFO overflow is
encountered and return the -EIO error code, which better indicates
the problem than -ETIMEDOUT that was returned previously in such
case.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>