staging: fsl-mc: fix resource_size.cocci warnings

Use resource_size() function on resource objects instead of
explicit computation.

This patch fixes the following coccinelle warning:

drivers/staging/fsl-mc/bus/dprc-driver.c:620:35-38: ERROR: Missing
resource_size with mc_dev -> regions

Signed-off-by: Cihangir Akturk <cakturk@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>