powerpc: Fix size calculation using resource_size()

The problem is the the calculation should be "end - start + 1" but the
plus one is missing in this calculation.

Fixes: 8626816 ("powerpc: add support for MPIC message register API")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/mpic_msgr.c

@@ -196,7 +196,7 @@ static int mpic_msgr_probe(struct platform_device *dev)
 
 	/* IO map the message register block. */
 	of_address_to_resource(np, 0, &rsrc);
-	msgr_block_addr = ioremap(rsrc.start, rsrc.end - rsrc.start);
+	msgr_block_addr = ioremap(rsrc.start, resource_size(&rsrc));
 	if (!msgr_block_addr) {
 		dev_err(&dev->dev, "Failed to iomap MPIC message registers");
 		return -EFAULT;