asm: Fix x86 assembly for inverse matrix operations

asm: Fix x86 assembly for inverse matrix operations

In commit 3175b63a0dfa290430f9f7eb651387788933a02b, Marek stopped
allocating the GLmatrix::inv field with malloc, instead embedding
it directly in the structure.  So, we need to drop a level of
indirection here and use (matrix pointer + MATRIX_INV) as the
inverse matrix array directly, rather than reading a pointer at
that offset and chasing it.

Fixes: 3175b63a0df ("mesa: don't allocate matrices with malloc")
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7889>