net: macb: fix error format in dev_err()

Errors are negative numbers. Using %u shows them as very large positive
numbers such as 4294967277 that don't make sense. Use the %d format
instead, and get a much nicer -19.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Fixes: b48e0bab ("net: macb: Migrate to devm clock interface")
Fixes: 93b31f48 ("net/macb: unify clock management")
Fixes: 421d9df0 ("net/macb: merge at91_ether driver into macb driver")
Fixes: aead88bd ("net: ethernet: macb: Add support for rx_clk")
Fixes: f5473d1d ("net: macb: Support clock management for tsu_clk")
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>