serial: qcom_geni: Fix variable naming

Commit 2aaa43c7 ("tty: serial: qcom-geni-serial: add support for
serial engine DMA") renamed rx_fifo member to rf_buf which caused a
build failure when b8caf69a ("tty: serial: qcom-geni-serial: fix
slab-out-of-bounds on RX FIFO buffer") from tty-linus was merged into
tty-next.

Fix the member variable name.

Fixes: 7a6aa989 ("Merge 6.2-rc5 into tty-next")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230123173857.40695-2-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/qcom_geni_serial.c

@@ -1055,11 +1055,11 @@ static int setup_fifos(struct qcom_geni_serial_port *port)
 	uport->fifosize =
 		(port->tx_fifo_depth * port->tx_fifo_width) / BITS_PER_BYTE;
 
-	if (port->rx_fifo && (old_rx_fifo_depth != port->rx_fifo_depth) && port->rx_fifo_depth) {
-		port->rx_fifo = devm_krealloc(uport->dev, port->rx_fifo,
-					      port->rx_fifo_depth * sizeof(u32),
-					      GFP_KERNEL);
-		if (!port->rx_fifo)
+	if (port->rx_buf && (old_rx_fifo_depth != port->rx_fifo_depth) && port->rx_fifo_depth) {
+		port->rx_buf = devm_krealloc(uport->dev, port->rx_buf,
+					     port->rx_fifo_depth * sizeof(u32),
+					     GFP_KERNEL);
+		if (!port->rx_buf)
 			return -ENOMEM;
 	}