tty: cpm_uart: use resource_size()

Use the resource_size function instead of manually calculating the
resource size.  This reduces the chance of introducing off-by-one errors.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Kumar Gala <galak@gate.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/serial/cpm_uart/cpm_uart_cpm2.c

@@ -61,7 +61,7 @@ void __iomem *cpm_uart_map_pram(struct uart_cpm_port *port,
 	void __iomem *pram;
 	unsigned long offset;
 	struct resource res;
-	unsigned long len;
+	resource_size_t len;
 
 	/* Don't remap parameter RAM if it has already been initialized
 	 * during console setup.
@@ -74,7 +74,7 @@ void __iomem *cpm_uart_map_pram(struct uart_cpm_port *port,
 	if (of_address_to_resource(np, 1, &res))
 		return NULL;
 
-	len = 1 + res.end - res.start;
+	len = resource_size(&res);
 	pram = ioremap(res.start, len);
 	if (!pram)
 		return NULL;