r100: Use _mesa_get_format_base_format in radeon_update_wrapper

r100: Use _mesa_get_format_base_format in radeon_update_wrapper

The wrapper is for a renderbuffer around a texture.  Textures can have
formats (e.g., 3) that aren't valide for API generated renderbuffers.
_mesa_base_fbo_format will return 0, but _mesa_get_format_base_format
will return the base format of RGB.

Fixes a crashes in piglit tests fbo-alphatest-formats (all subtests
pass) and fbo-colormask-formats (some subtests pass, some fail).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>