net: wwan: core: init port type string array using enum values

This array is indexed by port type. Make it self-descriptive by using
the port type enum values as indices in the array initializer.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>