tty: serial: amba-pl011: remove set but unused variable

Fix the following warning:
drivers/tty/serial/amba-pl011.c: In function check_apply_cts_event_workaround:
drivers/tty/serial/amba-pl011.c:1461:15: warning: variable dummy_read set but not used [-Wunused-but-set-variable]

The data read is useless and can be dropped.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Link: https://lore.kernel.org/r/1575619526-34482-1-git-send-email-wangxiongfeng2@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -1452,8 +1452,6 @@ static void pl011_modem_status(struct uart_amba_port *uap)
 
 static void check_apply_cts_event_workaround(struct uart_amba_port *uap)
 {
-	unsigned int dummy_read;
-
 	if (!uap->vendor->cts_event_workaround)
 		return;
 
@@ -1465,8 +1463,8 @@ static void check_apply_cts_event_workaround(struct uart_amba_port *uap)
 	 * single apb access will incur 2 pclk(133.12Mhz) delay,
 	 * so add 2 dummy reads
 	 */
-	dummy_read = pl011_read(uap, REG_ICR);
-	dummy_read = pl011_read(uap, REG_ICR);
+	pl011_read(uap, REG_ICR);
+	pl011_read(uap, REG_ICR);
 }
 
 static irqreturn_t pl011_int(int irq, void *dev_id)