x86: Fix fixmap ordering

The merge of the 32- and 64-bit fixmap headers made a latent
bug on x86-64 a real one: with the right config settings
it is possible for FIX_OHCI1394_BASE to overlap the FIX_BTMAP_*
range.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: <stable@kernel.org> # for 2.6.30.x
LKML-Reference: <4A4A0A8702000078000082E8@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>