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

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

BugLink: https://bugs.launchpad.net/bugs/1904450
[ Upstream commit 5026cf605143e764e1785bbf9158559d17f8d260 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: William Breathitt Gray <william.gray@canonical.com>