ALSA: asihpi: clean up a couple of build warnings

Variable dpcm is never used and hence can be removed. Variable
runtime is being assigned but is never read, so the assignment
is redundant and can be removed. Cleans up two clang warnings:

Value stored to 'dpcm' is never read
Value stored to 'runtime' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>