alsa-mixer: Don't let "Mic Jack Mode" alone create a "Line In" path

alsa-mixer: Don't let "Mic Jack Mode" alone create a "Line In" path

The IDT/Sigmatel codec driver often creates a "Mic Jack Mode" for
every mic jack, so it can change functionality between Mic and Line In.

However, as the "Mic Jack" is the standard naming, our current solution
does not make the Line In port unavailable when nothing is plugged in.

This patch makes the "Line In" port not to be created just because there
is a "Mic Jack Mode" that could be set to "Line". This makes the behaviour
consistent with e g "Dock Mic Jack Mode", "Front Mic Jack Mode" etc, where
we don't create a "Dock Line" or "Dock Mic" port either.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>