tty: n_smux: Change external modem name for SSR

The modem driver that handles subsystem restart uses the name
"external_modem" for the external modem.

Change-Id: I4a8199bd259b1aa2ee9310fc29c55c9db4f4cbab
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>
1 file changed