ALSA: hda - Remove the use of set_fs()

set_fs() is used in HD-audio vmaster code to retrieve the TLV data of
each slave kctl.  Since the slave is supposed to be a standard amp
kctl, we can call directly the supposed tlv callback instead of the
indirect call, so that we can remove the set_fs() hack.

Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>