[AArch64] Remove a duplicate call to setHasWinCFI. NFCI.

The function already has a cleanup scope that calls the same whenever
the function is exited. When reading the code, seeing that this return
codepath has an explicit call while other return paths lack it is
confusing.

In the hypothetical case of a function having a prologue that
set the HasWinCFI flag in the MF, but the epilogue containing no
WinCFI instructions, the HasWinCFI flag in the MF would end up reset back
to false.

Differential Revision: https://reviews.llvm.org/D88636