objtool: Rename find_containing_func()

For consistency; we have:

  find_symbol_by_offset() / find_symbol_containing()
  find_func_by_offset()   / find_containing_func()

fix that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.558470724@infradead.org