bus/fsl_mc: Do not rely on caller to provide non NULL mc_io

Before destroying the mc_io, check first that it was
allocated.

Reviewed-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Diana Craciun <diana.craciun@oss.nxp.com>
Link: https://lore.kernel.org/r/20200929085441.17448-11-diana.craciun@oss.nxp.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>