ALSA: aloop: Describe units of variables

Describe the unit of the variables used to calculate the hw pointer
depending on jiffies ticks.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Link: https://lore.kernel.org/r/20191120174955.6410-2-andrew_gabbasov@mentor.com


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