PCM Midlevel
Fix suggested by Benjamin Herrenschmidt <benh@kernel.crashing.org>

On architectures like PPC, char is handled as 'unsigned char', thus the
pcm_format_data table entries with -1 give a positive 255.  This causes
Oops with OSS-emulation on such architectures.

The patch simply adds the right signed/unsigned prefix to fix this problem.
Signed-off-by: Takashi Iwai <tiwai@suse.de>