[WATCHDOG] use resource_size()

Use resource_size().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Kevin Hilman <khilman@ti.deeprootsystems.com>
Cc: Ulrik Bech Hald <ubh@ti.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Vincent Sanders <support@simtec.co.uk>
Acked-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>