[media] omap: fix compilation if !VIDEO_OMAP2_VOUT_VRFB

When CONFIG_VIDEO_OMAP2_VOUT_VRFB is disabled, the compilation
will fail, as the function stubs are wrong. Also, as they weren't
declared as static inline, lots of warnings will be generated.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>