ALSA: hdsp: Make the firmware loading ioctl a bit more readable

ALSA: hdsp: Make the firmware loading ioctl a bit more readable

The firmware loading ioctl that is implemented for hdsp hwdep device
takes the reference of the address pointer, hence the current code is
rather confusing.  Also, due to the recent change in uapi header,
sparse also complains about the cast.

This patch tries to improve the readability by converting the
straightforward copy_from_user of the whole struct (which contains
only the pointer).

Fixes: 39ff8bddd7f7 ("ALSA: hdsp: Make uapi/hdsp.h compilable again")
Link: https://lore.kernel.org/r/20200202090724.18232-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>