ALSA: emu10k1: Fix missing __force annotation for user/kernel pointer cast

The cast between user-space and kernel-space needs an explicit __force
prefix, but it's missing in many places in emu10k1 driver code.

Spotted by sparse as a warning like:
  sound/pci/emu10k1/emufx.c:529:33: warning: cast removes address space of expression

Signed-off-by: Takashi Iwai <tiwai@suse.de>