[CodeGen] Fix restore blocks' BasicBlock information in branch relaxation

In branch relaxation pass, restore blocks are created and placed before
the jump destination if indirect branches are required. For example:

        foo
        sd      s11, 0(sp)
        jump    .restore, s11
        bar
        bar
        bar
        j       .dest
.restore:
        ld      s11, 0(sp)
.dest:
        baz

The BasicBlock information of the restore MachineBasicBlock should be
identical to the dest MachineBasicBlock.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D131863