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: bb5f86e ("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>

Author: nathanchance

sound/pci/hda/tas2781_hda_spi.c

@@ -105,18 +105,17 @@ static const struct regmap_config tasdevice_regmap = {
 static int tasdevice_spi_switch_book(struct tasdevice_priv *tas_priv, int reg)
 {
 	struct regmap *map = tas_priv->regmap;
-	int ret;
 
 	if (tas_priv->cur_book != TASDEVICE_BOOK_ID(reg)) {
-		ret = regmap_write(map, TASDEVICE_BOOKCTL_REG,
-				   TASDEVICE_BOOK_ID(reg));
+		int ret = regmap_write(map, TASDEVICE_BOOKCTL_REG,
+				       TASDEVICE_BOOK_ID(reg));
 		if (ret < 0) {
 			dev_err(tas_priv->dev, "Switch Book E=%d\n", ret);
 			return ret;
 		}
 		tas_priv->cur_book = TASDEVICE_BOOK_ID(reg);
 	}
-	return ret;
+	return 0;
 }
 
 int tasdevice_spi_dev_read(struct tasdevice_priv *tas_priv,