ASoC: soc-core: cleanup cppcheck warning at snd_soc_add_controls()

This patch cleanups below cppcheck warning.

sound/soc/soc-core.c:2239:6: style: The scope of the variable 'err' can be reduced. [variableScope]
 int err, i;
     ^

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87r1fhyl6f.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>