rapidio/rio_mport_cdev: use array_size() helper in copy_{from,to}_user()

rapidio/rio_mport_cdev: use array_size() helper in copy_{from,to}_user()

Use array_size() helper instead of the open-coded version in
copy_{from,to}_user().  These sorts of multiplication factors need to be
wrapped in array_size().

This issue was found with the help of Coccinelle and, audited and fixed
manually.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Link: http://lkml.kernel.org/r/20200616183050.GA31840@embeddedor
Addresses-KSPP-ID: https://github.com/KSPP/linux/issues/83
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>