gpu: nvgpu: Fix off-by-one error in PDE calculations

The number of entries in the next level PDE data structure was one
half of what was needed since the bit shift was 1 bit too small.

Change-Id: Id4981f230dd206ae94336cddab117312e143e6a1
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/740727
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>

drivers/gpu/nvgpu/gk20a/mm_gk20a.c

@@ -2134,7 +2134,7 @@ static int update_gmmu_level_locked(struct vm_gk20a *vm,
 				int num_entries =
 					1 <<
 					 (l->hi_bit[pgsz_idx]
-					  - l->lo_bit[pgsz_idx]);
+					  - l->lo_bit[pgsz_idx] + 1);
 				pte->entries =
 					kzalloc(sizeof(struct gk20a_mm_entry) *
 						num_entries, GFP_KERNEL);