[Hexagon] Be careful about anti-dependencies with a call in packetizer

In a case like
  J2_callr <ga:@foo>, %R0<imp-use>, ...
  R0<def> = ...
the anti-dependency on R0 cannot be ignored and the two instructions
cannot be packetized together, since if they were, the assignment to
R0 would take place before the call.

llvm-svn: 268776