ALSA: emu10k1: Use workqueue instead of kthread for emu1010 fw polling

This patch is a cleanup of EMU1010 dock probing code in emu10k1 driver
to use work instead of kthread in a loop.  The work is lighter and
easier to control than kthread, in general.

Instead of a loop with the explicit sleep, we do simply
delayed-schedule the work.  At suspend/resume callbacks, the work is
canceled and restarted, respectively.

Signed-off-by: Takashi Iwai <tiwai@suse.de>