[ALSA] pcxhr - Fix a compiler warning on 64bit architectures

The patch fixes a conpile warning on 64bit architectures, caused by
different sizes of size_t . Since size_t is unsigned I permited
myself to cange the format, too.

Signed-off-by: Henrik Kretzschmar <henne@nachtwindheim.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>