aco: don't consider a phi trivial if same's register doesn't match the def
For example:
s2: %688:s[32-33] = p_linear_phi %3:s[10-11], %688:s[32-33]would have been considered trivial.
For example:
s2: %688:s[32-33] = p_linear_phi %3:s[10-11], %688:s[32-33]would have been considered trivial.