drm/nouveau: set legacy bios data before parsing the structure

Commit 767baf82 drm/nouveau: remove some more unnecessary legacy bios code

has introduced a regression my misplacing the code that sets the major/chip
versions, which are used whist parsing the bmp/bit structure in vbios

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>