sha1_file.c: fix typo

it's != its
Signed-off-by: NFelipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -801,7 +801,7 @@ unsigned char* use_pack(struct packed_git *p,
 	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.