drm/gem: fix build for mm_get_unmapped_area() call after backmerge

drm/gem: fix build for mm_get_unmapped_area() call after backmerge

Commit 9ac09bb9feac ("mm: consistently use current->mm in
mm_get_unmapped_area()") upstream dropped a parameter from
mm_get_unmapped_area() while commit 99bda20d6d4c ("drm/gem: Introduce
drm_gem_get_unmapped_area() fop") in drm-misc-next added a new user.

Drop the extra parameter from the call.

Fixes: 7f790dd21a93 ("Merge drm/drm-next into drm-misc-next")
Cc: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Link: https://patch.msgid.link/20251215092706.3218018-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>