gianfar: Fix sparse warnings

This patch fixes following sparse warnings:

  CHECK   gianfar_ethtool.c
gianfar_ethtool.c:610:26: warning: symbol 'gfar_ethtool_ops' was not declared. Should it be static?
  CHECK   gianfar_mii.c
gianfar_mii.c:108:35: warning: cast adds address space to expression (<asn:2>)
gianfar_mii.c:119:35: warning: cast adds address space to expression (<asn:2>)
gianfar_mii.c:128:35: warning: cast adds address space to expression (<asn:2>)
gianfar_mii.c:272:5: warning: cast removes address space of expression
gianfar_mii.c:271:15: warning: cast adds address space to expression (<asn:2>)
gianfar_mii.c:340:11: warning: cast adds address space to expression (<asn:2>)
  CHECK   gianfar_sysfs.c
gianfar_sysfs.c:84:1: warning: symbol 'dev_attr_bd_stash' was not declared. Should it be static?
gianfar_sysfs.c:133:1: warning: symbol 'dev_attr_rx_stash_size' was not declared. Should it be static?
gianfar_sysfs.c:175:1: warning: symbol 'dev_attr_rx_stash_index' was not declared. Should it be static?
gianfar_sysfs.c:213:1: warning: symbol 'dev_attr_fifo_threshold' was not declared. Should it be static?
gianfar_sysfs.c:250:1: warning: symbol 'dev_attr_fifo_starve' was not declared. Should it be static?
gianfar_sysfs.c:287:1: warning: symbol 'dev_attr_fifo_starve_off' was not declared. Should it be static?

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>