can: mcp251xfd: mcp251xfd_handle_rxif_ring(): first increment RX tail pointer in HW, then in driver

The previous patch fixes a TEF vs. TX race condition, by first updating the TEF
tail pointer in hardware, and then updating the driver internal pointer.

The same pattern exists in the RX-path, too. This should be no problem, as the
driver accesses the RX-FIFO from the interrupt handler only, thus the access is
properly serialized. Fix the order here, too, so that the TEF- and RX-path look
similar.

Fixes: 1f652bb6bae7 ("can: mcp25xxfd: rx-path: reduce number of SPI core requests to set UINC bit")
Link: https://lore.kernel.org/r/20210105214138.3150886-3-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -1552,10 +1552,8 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 
 		/* Increment the RX FIFO tail pointer 'len' times in a
 		 * single SPI message.
-		 */
-		ring->tail += len;
-
-		/* Note:
+		 *
+		 * Note:
 		 *
 		 * "cs_change == 1" on the last transfer results in an
 		 * active chip select after the complete SPI
@@ -1571,6 +1569,8 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 		last_xfer->cs_change = 1;
 		if (err)
 			return err;
+
+		ring->tail += len;
 	}
 
 	return 0;