radv: fix identity swizzle handling
radv: fix identity swizzle handling

The identity swizzle should operate exactly
like an .r = R, .g = G, .b = B, .a = A swizzle.

This fixes a bunch of the 16-bit BGRA blit tests
dEQP-VK.api.copy_and_blit.blit_image.all_formats.b4g4r4a4*

Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler