i3c: dw: Create a generic fifo read function

In a future change we'll want to read from the IBI FIFO too, so turn
dw_i3c_read_rx_fifo() into a generic read with the FIFO register as a
parameter.
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/827204789583dd86addffb47ecaeab9d67cf95d5.1680161823.git.jk@codeconstruct.com.auSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/i3c/master/dw-i3c-master.c

@@ -318,18 +318,24 @@ static void dw_i3c_master_wr_tx_fifo(struct dw_i3c_master *master,
 	}
 }
 
-static void dw_i3c_master_read_rx_fifo(struct dw_i3c_master *master,
-				       u8 *bytes, int nbytes)
+static void dw_i3c_master_read_fifo(struct dw_i3c_master *master,
+				    int reg,  u8 *bytes, int nbytes)
 {
-	readsl(master->regs + RX_TX_DATA_PORT, bytes, nbytes / 4);
+	readsl(master->regs + reg, bytes, nbytes / 4);
 	if (nbytes & 3) {
 		u32 tmp;
 
-		readsl(master->regs + RX_TX_DATA_PORT, &tmp, 1);
+		readsl(master->regs + reg, &tmp, 1);
 		memcpy(bytes + (nbytes & ~3), &tmp, nbytes & 3);
 	}
 }
 
+static void dw_i3c_master_read_rx_fifo(struct dw_i3c_master *master,
+				       u8 *bytes, int nbytes)
+{
+	return dw_i3c_master_read_fifo(master, RX_TX_DATA_PORT, bytes, nbytes);
+}
+
 static struct dw_i3c_xfer *
 dw_i3c_master_alloc_xfer(struct dw_i3c_master *master, unsigned int ncmds)
 {