s3cmci: use resource_size() instead of local macro

Replace the local definition RESSIZE() with the standard resource_size()
call for getting the size of a struct resource.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>