ALSA: rawmidi: Embed struct device

Like previous patches, this changes the device management for rawmidi,
embedding the struct device into struct snd_rawmidi.  The required
change is more or less same as hwdep device.

The currently unused dev field is reused as the new embedded struct
field now.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>