drm/xe/svm: fix dereferencing error pointer in drm_gpusvm_range_alloc()

xe_svm_range_alloc() returns ERR_PTR(-ENOMEM) on failure and there is a
dereference of "range" after that:

	-->     range->gpusvm = gpusvm;

In xe_svm_range_alloc(), when memory allocation fails return NULL
instead to handle this situation.

Fixes: 99624bdf ("drm/gpusvm: Add support for GPU Shared Virtual Memory")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/adaef4dd-5866-48ca-bc22-4a1ddef20381@stanley.mountain/


Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250323124907.3946370-1-harshit.m.mogalapalli@oracle.com