staging: kpc2000: fix resource size calculation

The code is calculating the resource size wrong because it should be
inclusive of the "res->end" address.  In other words, "end - start + 1".
We can just use the resource_size() function to do it correctly.

Fixes: 7dc7967f ("staging: kpc2000: add initial set of Daktronics drivers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>