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/20251103-work-creds-guards-prepare_creds-v1-5-b447b82f2c9b@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/coredump.c

@@ -1197,8 +1197,8 @@ void vfs_coredump(const kernel_siginfo_t *siginfo)
 	}
 
 close_fail:
-	coredump_cleanup(&cn, &cprm);
 	revert_creds(old_cred);
+	coredump_cleanup(&cn, &cprm);
 	return;
 }