ALSA: ctxfi: changed void * to struct hw *

in the code we have void *hw and while using we are always typecasting
it to (struct hw *). it is better to use void type of pointer when we
store different types of pointer , but in this code we are only having
struct hw.
So changed all the relevant reference of void *hw to struct hw *hw,
without any modification of the existing code logic.
the next patch of the series will remove the typecasting which is
not required now.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>