net: macb: Fix coding style error message

checkpatch.pl gave the following error:

ERROR: space required before the open parenthesis '('
+	for(; p < end; p++, offset += 4)

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Signed-off-by: David S. Miller <davem@davemloft.net>