tgsi: (trivial) only verify target for is_tex instructions

tgsi: (trivial) only verify target for is_tex instructions

d3d10 state tracker does not encode (valid) target (only offsets are
really used from the texture bits), since that information always comes
from the sview dcl, and not the instruction (note the meaning of target
is actually slightly different between gl and d3d10 in any case, because
d3d10 target does never include shadow bit).
Also move the msaa sampler identification as well - would need to set that
on the sview not sampler, so while this does not fix it make it at least
obvious it won't work with sample instructions.