serial: core: return early on unsupported ioctls

Drivers can return -ENOIOCTLCMD when an ioctl is not recognised to tell
the upper layers to continue looking for a handler.

This is not the case for the RS485 and ISO7816 ioctls whose handlers
should return -ENOTTY directly in case a serial driver does not
implement the corresponding methods.

Fixes: a5f276f1 ("serial_core: Handle TIOC[GS]RS485 ioctls.")
Fixes: ad8c0eaa ("tty/serial_core: add ISO7816 infrastructure")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407095208.31838-9-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>