vp9: Check for invalid parameter for color space SRGB

Check for invalid parameter for color space SRGB, and add
additional assert in write_bitdepth_colorspace_sampling()
for the case cm->color_space == VPX_CS_SRGB.

Bug: b:418060861
Change-Id: I56c4e78fdc3057e34fdb84a3a48079eb138207fd
2 files changed