staging: fsl-mc: add device release callback

When hot unplugging a mc-bus device the kernel displays
this pertinent message, followed by a stack dump:
    "Device 'foo.N' does not have a release() function,
     it is broken and must be fixed."
Add the required callback to fix and drop the now
uneeded explicit freeing.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Stuart Yoder <stuart.yoder@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>