bus: fsl-mc: Only warn once about errors on device unbind

If a platform driver's remove function returns an error code, this
results in a (generic and little helpful) error message. Otherwise the
value is ignored.

As fsl_mc_driver_remove() already emit an error message, return 0 also
in the error case. The only effect is to suppress the device core's
error message.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Tested-by: Ioana Ciornei <ioana.ciornei@nxp.com> # sanity checks
Reviewed-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Tested-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>