ALSA: emu10k1: Make uapi/emu10k1.h compilable again

ALSA: emu10k1: Make uapi/emu10k1.h compilable again

Recently we updated the content in alsa-lib uapi header files by just
copying from the latest Linus kernel uapi/*.h, and noticed that it
broke the build of some alsa-tools programs.  The reason is that we
used to have a modified version in the past, so that the program can
be built without referring to the unexported stuff like
snd_ctl_elem_id or __user prefix.

This patch attempts to restore that, i.e. dropping the stuff that
can't be referred in the user-space.  For adapting the changes in
uapi/emu10k1.h, the emu10k1 driver code is also slightly modified.
Most of changes are pointer cast.

Link: https://lore.kernel.org/r/20191220153415.2740-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>