The SUN GISB arbiter was added with the wrong compatible string, leading to
using the wrong register layout, use the correct compatible string for this
chip: brcm,bcm7435-gisb-arb.

Fixes: 8394968be4c7 ("MIPS: BMIPS: Add BCM7435 dtsi")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: blogic@openwrt.org
Cc: cernekee@gmail.com
Cc: jogo@openwrt.org
Cc: jaedon.shin@gmail.com
Cc: pgynther@google.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12285/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>