ASoC: fsl: imx-sgtl5000: Add .remove back

Commit e8f00c1b (Merge remote-tracking branch 'asoc/fix/fsl' into asoc-devm)
fixed a conflict, but missed to add the .remove function back,which causes the
following build warning:

sound/soc/fsl/imx-sgtl5000.c:185:12: warning: 'imx_sgtl5000_remove' defined but not used [-Wunused-function]

Fix the warning by adding the .remove function back.

Reported-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>