bfd: aarch64: Fix BTI stub optimization PR30957

The instruction was looked up in the wrong input file (file of branch
source instead of branch target) when optimizing away BTI stubs in

  commit 5834f36d93cabf1a8bcc7dd7654141aed3d296bc
  bfd: aarch64: Optimize BTI stubs PR30076

This can cause adding BTI stubs when they are not necessary or removing
them when they are (the latter is a correctness issue but it is very
unlikely in practice).

Fixes bug 30957.
1 file changed