ASoC: fsl_sai: Add missing return 0 in remove()

Build warning being reported:
    sound/soc/fsl/fsl_sai.c: In function 'fsl_sai_remove':
    sound/soc/fsl/fsl_sai.c:921:1: warning: no return statement in
    function returning non-void [-Wreturn-type]

So this patch just adds a "return 0" to fix it.

Fixes: 812ad463

 ("ASoC: fsl_sai: Add support for runtime pm")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>