can: m_can: m_can_do_rx_poll(): fix extraneous msg loss warning

Message loss from RX FIFO 0 is already handled in
m_can_handle_lost_msg(), with netdev output included.

Removing this warning also improves driver performance under heavy
load, where m_can_do_rx_poll() may be called many times before this
interrupt is cleared, causing this message to be output many
times (thanks Mariusz Madej for this report).

Fixes: e0d1f48 ("can: m_can: add Bosch M_CAN controller support")
Link: https://lore.kernel.org/r/20210303103151.3760532-1-torin@maxiluxsystems.com
Reported-by: Mariusz Madej <mariusz.madej@xtrack.com>
Signed-off-by: Torin Cooper-Bennun <torin@maxiluxsystems.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -501,9 +501,6 @@ static int m_can_do_rx_poll(struct net_device *dev, int quota)
 	}
 
 	while ((rxfs & RXFS_FFL_MASK) && (quota > 0)) {
-		if (rxfs & RXFS_RFL)
-			netdev_warn(dev, "Rx FIFO 0 Message Lost\n");
-
 		m_can_read_fifo(dev, rxfs);
 
 		quota--;