ALSA: isa/wavefront: remove redundant assignment to pointer bptr

The pointer bptr is being assigned a value that is never read
and it is being updated in the next statement with a new value.
The initialization is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>