swr: only broadcast color0 value, not all color values

swr: only broadcast color0 value, not all color values

The way that dual-source blending is described for GLES2 is very odd,
and we end up with a shader that both has this property set *and* has a
color1 value to be used as the second source. While changing the state
tracker is an option, it seems more reliable to verify that the
broadcast is only done on color0.

Fixes arb_blend_func_extended-fbo-extended-blend-pattern_gles2

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Tim Rowley <timothy.o.rowley@intel.com>