serial: pl011: (cosmetic) remove superfluous register write

In pl011_rx_chars() if pl011_dma_rx_trigger_dma() succeeds it will disable
the receive interrupt, no need to do this again.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -1214,8 +1214,8 @@ __acquires(&uap->port.lock)
 			dev_dbg(uap->port.dev, "could not trigger RX DMA job "
 				"fall back to interrupt mode again\n");
 			uap->im |= UART011_RXIM;
+			writew(uap->im, uap->port.membase + UART011_IMSC);
 		} else {
-			uap->im &= ~UART011_RXIM;
 #ifdef CONFIG_DMA_ENGINE
 			/* Start Rx DMA poll */
 			if (uap->dmarx.poll_rate) {
@@ -1227,8 +1227,6 @@ __acquires(&uap->port.lock)
 			}
 #endif
 		}
-
-		writew(uap->im, uap->port.membase + UART011_IMSC);
 	}
 	spin_lock(&uap->port.lock);
 }