powerpc/powernv: use resource_size

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

The semantic patch that makes these changes 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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1577900990-8588-11-git-send-email-Julia.Lawall@inria.fr