fbdev: cg14fb: use resource_size

fbdev: cg14fb: use resource_size

Use resource_size rather than a verbose computation on
the end and start fields.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@ struct resource ptr; @@
- (ptr.end - ptr.start + 1)
+ resource_size(&ptr)
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
[b.zolnierkie: minor patch summary fixup]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1577900990-8588-8-git-send-email-Julia.Lawall@inria.fr