bus: brcmstb_gisb: Use register offsets with writes too

This commit corrects the bug introduced in commit f8083587
("bus: brcmstb_gisb: Look up register offsets in a table") such
that gisb_write() translates the register enumeration into an
offset from the base address for writes as well as reads.

Fixes: f8083587 ("bus: brcmstb_gisb: Look up register offsets in a table")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

drivers/bus/brcmstb_gisb.c

 /*
- * Copyright (C) 2014 Broadcom Corporation
+ * Copyright (C) 2014-2017 Broadcom
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -127,9 +127,9 @@ static void gisb_write(struct brcmstb_gisb_arb_device *gdev, u32 val, int reg)
 		return;
 
 	if (gdev->big_endian)
-		iowrite32be(val, gdev->base + reg);
+		iowrite32be(val, gdev->base + offset);
 	else
-		iowrite32(val, gdev->base + reg);
+		iowrite32(val, gdev->base + offset);
 }
 
 static ssize_t gisb_arb_get_timeout(struct device *dev,