Fixes unhandled register write in gianfar_ethtool.c.
Fixes following endianess related functional issues,
reported by sparse as well, i.e.:

gianfar_ethtool.c:1058:33: warning:
    incorrect type in argument 1 (different base types)
    expected unsigned int [unsigned] [usertype] value
    got restricted __be32 [usertype] ip4src

gianfar_ethtool.c:1164:33: warning:
    restricted __be16 degrades to integer

gianfar_ethtool.c:1669:32: warning:
    invalid assignment: ^=
    left side has type restricted __be16
    right side has type int

Solves all the sparse warnings for mixig normal pointers
with __iomem pointers for gianfar_ptp.c, i.e.:
gianfar_ptp.c:163:32: warning:
    incorrect type in argument 1 (different address spaces)
    expected unsigned int [noderef] <asn:2>*addr
    got unsigned int *<noident>
Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>