ALSA: hda/tas2781: Fix the symbol was not declare warning reported by kernel test...

ALSA: hda/tas2781: Fix the symbol was not declare warning reported by kernel test robot

After commit 28a09d9e42c5 ("ALSA: hda/tas2781: Create an independent lib
to save the shared parts for both SPI and I2C driver") created a separated
lib for both hda-i2c and hda-spi driver, which caused this issue.
sparse warnings: (new ones prefixed by >>)
>> sound/pci/hda/tas2781_hda_spi.c:496:25: sparse: sparse: symbol
   'tas2781_snd_ctls' was not declared. Should it be static?
>> sound/pci/hda/tas2781_hda_spi.c:505:25: sparse: sparse: symbol
   'tas2781_prof_ctl' was not declared. Should it be static?
>> sound/pci/hda/tas2781_hda_spi.c:512:25: sparse: sparse: symbol
   'tas2781_dsp_ctls' was not declared. Should it be static?

Fixes: 28a09d9e42c5 ("ALSA: hda/tas2781: Create an independent lib to save the shared parts for both SPI and I2C driver")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-kbuild-all/202505130420.vr9yDI3k-lkp@intel.com/__;!!G3vK!URphGMMfZ2erCLfJdETofl0O1mTSydDLLJ6inMIYWYUDUKYef_IuLvI7pnYj3Mx-4LRIi4BJEw$
Signed-off-by: Shenghao Ding <shenghao-ding@ti.com>
Link: https://patch.msgid.link/20250513071721.1090-1-shenghao-ding@ti.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>