i965: Fix BLORP sRGB MSAA overrides to cope with X vs. A formats.

i965: Fix BLORP sRGB MSAA overrides to cope with X vs. A formats.

The logic in brw_blorp_surface_info::set uses brw_format_for_mesa_format
for source surfaces, and brw->render_target_format[] for destination
surfaces.  We should do the same in the sRGB MSAA overrides.

Currently, this isn't a problem, since SRGB MSAA buffers are all RGBA.
The next commit will introduce RGBX SRGB MSAA buffers, at which point
we need to get the RGBX -> RGBA format overrides for rendering right.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>