[ScheduleDAGInstrs] Call adjustSchedDependency in more cases

This removes a condition and the corresponding FIXME comment, because
the Hexagon assertion it refers to has apparently been fixed, probably
by D76134.

NFCI. This just gives targets the opportunity to adjust latencies that
were set to 0 by the generic code because they involve "implicit pseudo"
operands.

Differential Revision: https://reviews.llvm.org/D112306