[InstrProf] Allow CSIRPGO function entry coverage

The flag `-fcs-profile-generate` for enabling CSIRPGO moves the pass
`pgo-instrumentation` after inlining. Function entry coverage works fine
with this change, so remove the assert. I had originally left this
assert in because I had not tested this at the time.

Reviewed By: davidxl, MaskRay

Differential Revision: https://reviews.llvm.org/D129407