[SelectionDAG] make INLINEASM_BR use MachineBasicBlocks instead of BlockAddresses

As part of re-architecting callbr to no longer use blockaddresses
(https://reviews.llvm.org/D129288), we don't really need them in MIR.
They make comparing MachineBasicBlocks of indirect targets during
MachineVerifier a PITA.

Suggested by @efriedma from the discussion:
https://reviews.llvm.org/D130290#3669531

Reviewed By: efriedma, void

Differential Revision: https://reviews.llvm.org/D130316