[ALSA] Fix 'discards qualifiers' compile warnings in pcm.h

Fixed cast messes in pcm.h.
    include/sound/pcm.h: In function ‘hw_param_interval_c’:
    include/sound/pcm.h:800: warning: passing argument 1 of ‘hw_param_interval’ discards qualifiers from pointer target type
Simply redefine the inline functions again for const pointers.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>