Until now, we hardcoded the internal format to GL_RGBA and used the
internal format returned by pixel_format_to_gl() as the format for
checking the texture size and format we're asked to create.
Let's use the proper internal format/format from now on.
This is needed as a later patch introduces DEPTH and DEPTH_STENCIL
textures.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit ec45f60ee2545f88302da314bcdbe1439c4ba9c9)