sha1_file.c: fix typo

it's != its

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/sha1_file.c b/sha1_file.c
index 5b6e0f6..032300c 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -801,7 +801,7 @@
 	if (p->pack_fd == -1 && open_packed_git(p))
 		die("packfile %s cannot be accessed", p->pack_name);
 
-	/* Since packfiles end in a hash of their content and its
+	/* Since packfiles end in a hash of their content and it's
 	 * pointless to ask for an offset into the middle of that
 	 * hash, and the in_window function above wouldn't match
 	 * don't allow an offset too close to the end of the file.