ALSA: hda: tas2781-spi: Fix -Wsometimes-uninitialized in tasdevice_spi_switch_book()

ALSA: hda: tas2781-spi: Fix -Wsometimes-uninitialized in tasdevice_spi_switch_book()

Clang warns (or errors with CONFIG_WERROR=y):

  sound/pci/hda/tas2781_hda_spi.c:110:6: error: variable 'ret' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
    110 |         if (tas_priv->cur_book != TASDEVICE_BOOK_ID(reg)) {
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  sound/pci/hda/tas2781_hda_spi.c:119:9: note: uninitialized use occurs here
    119 |         return ret;
        |                ^~~
  sound/pci/hda/tas2781_hda_spi.c:110:2: note: remove the 'if' if its condition is always true
    110 |         if (tas_priv->cur_book != TASDEVICE_BOOK_ID(reg)) {
        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  sound/pci/hda/tas2781_hda_spi.c:108:9: note: initialize the variable 'ret' to silence this warning
    108 |         int ret;
        |                ^
        |                 = 0

Sink the declaration of ret into the if block and just return 0 at the
end of the function, as there is nothing to do if cur_book has already
been changed.

Fixes: bb5f86ea50ff ("ALSA: hda/tas2781: Add tas2781 hda SPI driver")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501192006.Hm9GmKiV-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20250120-tas2781_hda_spi-fix-wsometimes-uninitialized-v1-1-d7fd104aa63e@kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>