This means that "mixerctl" (no args) will generate a usage msg, even when
/dev/mixer cannot be opened (or any other device given via -d or $MIXERDEVICE)
While here, get rid of "goto usage" replacing the usage: with a
static inline void __dead function... The compiler ought to optimise
the calls into essentially the same code as existed with the goto version,
but this is much cleaner.
Also, mixerctl falls back on /dev/mixer0 if /dev/mixer cannot be opened.
(that is old code - probably from when /dev/mixer was first added)
It used to do that when called as mixerctl -d /dev/mixer or with
"MIXERDEVICE=/dev/mixer mixerctl...". No longer. Now the fallback (which
is probably obsolete now anyway) only happens when the user doesn't specify
any mixer device (by either method) and the default of /dev/mixer is used.
In other cases, only the device specified is tried.
887a30551e