pan/mdg: Use _VTX tag for texelFetch in frag shaders

Probably a misnomer, let's match what the blob seemingly does though? At
least in blit shaders?

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5782>
1 file changed