unwind: fix a bug in range updating of binary search

* unwind.c (print_stacktrace): Fix off-by-one error in binary search.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Luca Clementi <luca.clementi@gmail.com>
diff --git a/unwind.c b/unwind.c
index 0b8f0b0..c16fdd1 100644
--- a/unwind.c
+++ b/unwind.c
@@ -258,7 +258,7 @@
 				goto ret;
 			}
 			else if (ip < cur_mmap_cache->start_addr)
-				upper = mid - 1;
+				upper = mid;
 			else
 				lower = mid + 1;