mixer: simple - Unify simple_none: base_len() exception handling

mixer: simple - Unify simple_none: base_len() exception handling

Unify simple_none: base_len() exception handling:

1. In the "Input Source" and "3D Control" cases the base-name is the same
   as the full-name and base_len() simply returns strlen(name).
   Instead of returning 0 when the type is unknown, set the type to
   CTL_SINGLE and return strlen(name). This allows removing the special
   case for base_len() returning 0 in simple_event_add().

2. Move the special handling for "Capture Volume" and "Capture Switch"
   from simple_event_add() to base_len(), so that we handle all exceptions
   inside base_len(). Instead of handling some special cases in base_len()
   and other special cases in simple_event_add().

[jk - moved the "Capture Volume" and "Capture Switch" to "Input Source"
exceptions]

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>