staging: fsl-mc: Naming cleanup in fsl_mc-portal_allocate

mc_adev is a local variable for the allocated dpmcp object.
Renamed mc_adev as dpmcp_dev for clarity.

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>