objtool: Fix 32bit cross builds

Apparently there's people doing 64bit builds on 32bit machines.

Fixes: 74b873e4 ("objtool: Optimize find_rela_by_dest_range()")
Reported-by:  <youling257@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>