ASoC: da7218: fix boolreturn.cocci warnings

sound/soc/codecs/da7218.c:3214:9-10: WARNING: return of 0/1 in function 'da7218_volatile_register' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>