ARM: footbridge: fix VGA initialisation

It's no good setting vga_base after the VGA console has been
initialised, because if we do that we get this:

Unable to handle kernel paging request at virtual address 000b8000
pgd = c0004000
[000b8000] *pgd=07ffc831, *pte=00000000, *ppte=00000000
0Internal error: Oops: 5017 [#1] ARM
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.12.0+ #49
task: c03e2974 ti: c03d8000 task.ti: c03d8000
PC is at vgacon_startup+0x258/0x39c
LR is at request_resource+0x10/0x1c
pc : [<c01725d0>]    lr : [<c0022b50>]    psr: 60000053
sp : c03d9f68  ip : 000b8000  fp : c03d9f8c
r10: 000055aa  r9 : 4401a103  r8 : ffffaa55
r7 : c03e357c  r6 : c051b460  r5 : 000000ff  r4 : 000c0000
r3 : 000b8000  r2 : c03e0514  r1 : 00000000  r0 : c0304971
Flags: nZCv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment kernel

which is an access to the 0xb8000 without the PCI offset required to
make it work.

Fixes: cc22b4c18540 ("ARM: set vga memory base at run-time")
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: <stable@vger.kernel.org>