Fix requiredby output

This is a bit embarrassing. For example:
$ pacman -Qi mesa
...
Required By    : mesa  mesa  mesa  mesa  mesa  mesa

Something is clearly not right, and the problem was introduced in commit
0bc961. Fix the issue by getting the package name off the correct variable.

Signed-off-by: Dan McGee <dan@archlinux.org>

lib/libalpm/package.c

@@ -573,7 +573,7 @@ alpm_list_t SYMEXPORT *alpm_pkg_compute_requiredby(pmpkg_t *pkg)
 		}
 		pmpkg_t *cachepkg = i->data;
 		if(_alpm_dep_edge(cachepkg, pkg)) {
-			const char *cachepkgname = pkg->name;
+			const char *cachepkgname = cachepkg->name;
 			reqs = alpm_list_add(reqs, strdup(cachepkgname));
 		}
 	}