resource: add resource_size()

Avoid one-off errors by introducing a resource_size() function.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/resource.c b/kernel/resource.c
index 74af2d7..f5b518e 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -490,7 +490,7 @@
 {
 	switch (res->flags & (IORESOURCE_SIZEALIGN | IORESOURCE_STARTALIGN)) {
 	case IORESOURCE_SIZEALIGN:
-		return res->end - res->start + 1;
+		return resource_size(res);
 	case IORESOURCE_STARTALIGN:
 		return res->start;
 	default: