brcm63xx: replace nvram_buf with a properly initialized array

brcm63xx: replace nvram_buf with a properly initialized array

Use an empty nvram_header to tell wl that there is no nvram buf.
wl else might try to allocate huge amount of memory because the
bcm63xx's nvram does not match the expected structure and contains
random values.

Fixes the following warning on load of wl:

[    9.152000] WARNING: at mm/slab_common.c:377 kmalloc_slab+0x4c/0xc0()
[    9.160000] Modules linked in: wl(P+) wl_glue ipv6 gpio_keys_polled input_polldev button_hotplug input_core
[    9.168000] CPU: 0 PID: 366 Comm: kmodloader Tainted: P             3.10.49 #1
[    9.176000] Stack : 00000000 00000000 00000000 00000000 8034b77a 00000042 81ac9af0 c02e0000
[    9.176000]    8028bf70 802df31b 0000016e 8034af28 81ac9af0 c02e0000 c02e0000 81b39810
[    9.176000]    0000002d 8002c9d4 00000003 8002a3c8 802937a0 c02e0000 8028e528 81ab398c
[    9.176000]    00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    9.176000]    00000000 00000000 00000000 00000000 00000000 00000000 00000000 81ab3918
[    9.176000]    ...
[    9.212000] Call Trace:
[    9.216000] [<800224b8>] show_stack+0x48/0x70
[    9.220000] [<8002a538>] warn_slowpath_common+0x78/0xa8
[    9.224000] [<8002a5f0>] warn_slowpath_null+0x18/0x24
[    9.228000] [<8008145c>] kmalloc_slab+0x4c/0xc0
[    9.236000] [<80097258>] __kmalloc+0x20/0x10c
[    9.240000] [<80e23b90>] osl_malloc+0x24/0x6c [wl]
[    9.244000] [<80e15288>] nvram_init+0x54/0x164 [wl]
[    9.252000] [<80e08668>] si_pci_fixcfg+0x60c/0x9e8 [wl]
[    9.256000]
[    9.260000] ---[ end trace b5c4dbb046cf3c83 ]---

Reported-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Jonas Gorski <jogo@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41861 3c298f89-4303-0410-b956-a3cf2f4a3e73