omap3: zoom: use static for pointer passing

omap_zoom_wlan_data and zoom2_set_hs_extmute are not used beyond
the scope of zoom-peripherals directly, instead pointers are used.
make them static instead.

Fixes sparse warnings:
arch/arm/mach-omap2/board-zoom-peripherals.c:193:29: warning: symbol 'omap_zoom_wlan_data' was not declared. Should it be static?
arch/arm/mach-omap2/board-zoom-peripherals.c:245:6: warning: symbol 'zoom2_set_hs_extmute' was not declared. Should it be static?

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>