drm/msm: fix msm_gem_vma_new() allocations for managed GPUVMs

drm/msm: fix msm_gem_vma_new() allocations for managed GPUVMs

Since commit 3309323241fb ("drm/gpuvm: Kill drm_gpuva_init()") MSM
driver fails to init, failing with "[drm:msm_gpu_init] *ERROR* could not
allocate memptrs: -22" errors. The mentioned commit reworked the
function, but didn't take into account that op_map is initialized at the
top of the function, while ranges might change if GPUVM is managed by
the kernel.

Move op_mode initialization after finalizing all addresses and right
before the drm_gpuva_init_from_op() call.

Reported-by: Danct12 <danct12@disroot.org>
Fixes: 3309323241fb ("drm/gpuvm: Kill drm_gpuva_init()")
Suggested-by: Rob Clark <robin.clark@oss.qualcomm.com>
Reviewed-by: Rob Clark <robin.clark@oss.qualcomm.com>
Acked-by: Rob Clark <robin.clark@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250823-msm-fix-gpuvm-init-v1-1-e199cd5b1983@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>