spi: amd: Fix -Wuninitialized in amd_spi_exec_mem_op()

After commit e6204f3 ("spi: amd: Drop redundant check"), clang warns (or
errors with CONFIG_WERROR=y):

  drivers/spi/spi-amd.c:695:9: error: variable 'ret' is uninitialized when used here [-Werror,-Wuninitialized]
    695 |         return ret;
        |                ^~~
  drivers/spi/spi-amd.c:673:9: note: initialize the variable 'ret' to silence this warning
    673 |         int ret;
        |                ^
        |                 = 0
  1 error generated.

ret is no longer set on anything other than the default switch path.
Replace ret with a direct return of 0 at the end of the function and
-EOPNOTSUPP in the default case to resolve the warning.

Fixes: e6204f3 ("spi: amd: Drop redundant check")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501112315.ugYQ7Ce7-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://patch.msgid.link/20250111-spi-amd-fix-uninitialized-ret-v1-1-c66ab9f6a23d@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: nathanchance

drivers/spi/spi-amd.c

@@ -670,7 +670,6 @@ static int amd_spi_exec_mem_op(struct spi_mem *mem,
 			       const struct spi_mem_op *op)
 {
 	struct amd_spi *amd_spi;
-	int ret;
 
 	amd_spi = spi_controller_get_devdata(mem->spi->controller);
 
@@ -689,10 +688,10 @@ static int amd_spi_exec_mem_op(struct spi_mem *mem,
 		amd_spi_mem_data_out(amd_spi, op);
 		break;
 	default:
-		ret = -EOPNOTSUPP;
+		return -EOPNOTSUPP;
 	}
 
-	return ret;
+	return 0;
 }
 
 static const struct spi_controller_mem_ops amd_spi_mem_ops = {