coredump: move revert_cred() before coredump_cleanup()

There's no need to pin the credentials across the coredump_cleanup()
call. Nothing in there depends on elevated credentials.

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

fs/coredump.c

···
 	}
 
 close_fail:
-	coredump_cleanup(&cn, &cprm);
 	revert_creds(old_cred);
+	coredump_cleanup(&cn, &cprm);
 	return;
 }