pcm: ioplug: Use boundary for wrap around

pcm: ioplug: Use boundary for wrap around

if requested by the IO plugin

Without this changes an IO plugin is not able to report
that buffer_size frames were read from the buffer.
When the buffer was full this is a valid action and
has not to be handled as an under run.

For example when the hw_ptr will be updated with
hw_ptr += buffer_size
and it is using the buffer_size as wrap around
hw_ptr %= buffer_size
would result in the same value as before the add operation.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>