ARM: OMAP2+: Make some variables static

Fix sparse warnings:

arch/arm/mach-omap2/omap_hwmod_33xx_43xx_ipblock_data.c:532:25: warning: symbol 'am33xx_gpio_hwmod_class' was not declared. Should it be static?
arch/arm/mach-omap2/omap_hwmod_33xx_43xx_ipblock_data.c:542:19: warning: symbol 'am33xx_gpio1_hwmod' was not declared. Should it be static?
arch/arm/mach-omap2/omap_hwmod_33xx_43xx_ipblock_data.c:562:19: warning: symbol 'am33xx_gpio2_hwmod' was not declared. Should it be static?
arch/arm/mach-omap2/omap_hwmod_33xx_43xx_ipblock_data.c:582:19: warning: symbol 'am33xx_gpio3_hwmod' was not declared. Should it be static?

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>