Fix sparse warning:

arch/arm/mach-imx/mach-pcm037.c:407:30: warning: symbol
'pcm970_sja1000_platform_data' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Ma Feng <mafeng.ma@huawei.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>