net: gianfar: fix old-style declaration

Modern C standards expect the '__inline__' keyword to come before the return
type in a declaration, and we get a warning for this with "make W=1":

drivers/net/ethernet/freescale/gianfar.c:2278:1: error: 'inline' is not at beginning of declaration [-Werror=old-style-declaration]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>