x86/crash: 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>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/1577900990-8588-10-git-send-email-Julia.Lawall@inria.fr