pcm: Wrap hw_ptr to boundary in pcm_ioplug

The function snd_pcm_ioplug_hw_ptr_update() always increased the hw_ptr
by delta, without wrapping it to the boundary. This would lead to
problems when after many hours, the hw_ptr would overflow.

Signed-off-by: Luciano Montanaro <luciano.montanaro@magnetimarelli.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>