i2c: Use resource_size

Use the function resource_size, which reduces the chance of introducing
off-by-one errors in calculating the resource size.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
struct resource *res;
@@

- (res->end - res->start) + 1
+ resource_size(res)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>