ARM: OMAP2+: Make some functions static

Fix sparse warnings:

arch/arm/mach-omap2/pmic-cpcap.c:29:15: warning: symbol 'omap_cpcap_vsel_to_uv' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:43:15: warning: symbol 'omap_cpcap_uv_to_vsel' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:93:15: warning: symbol 'omap_max8952_vsel_to_uv' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:107:15: warning: symbol 'omap_max8952_uv_to_vsel' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:140:15: warning: symbol 'omap_fan535503_vsel_to_uv' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:155:15: warning: symbol 'omap_fan535508_vsel_to_uv' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:173:15: warning: symbol 'omap_fan535503_uv_to_vsel' was not declared. Should it be static?
arch/arm/mach-omap2/pmic-cpcap.c:192:15: warning: symbol 'omap_fan535508_uv_to_vsel' was not declared. Should it be static?

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