drm/nouveau: Removes unnecessary args check in nouveau_uvmm_sm_prepare

Checking `args` after calling `op_map_prepare` is unnecessary since
if `op_map_prepare` was to be called with  NULL args, it would lead
to a NULL pointer dereference, thus never hitting that check.

Hence remove the check and add a note to remind users of this function
to ensure that args != NULL when calling this function for a map
operation as it was suggested by Danilo [1].

[1] https://lore.kernel.org/lkml/6a1ebcef-bade-45a0-9bd9-c05f0226eb88@redhat.comSuggested-by: Danilo Krummrich <dakr@redhat.com>
Signed-off-by: Yuran Pereira <yuran.pereira@hotmail.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/GV1PR10MB65637F4BAABFE2D8E261E1DCE8B0A@GV1PR10MB6563.EURPRD10.PROD.OUTLOOK.COM

drivers/gpu/drm/nouveau/nouveau_uvmm.c

@@ -608,6 +608,9 @@ op_unmap_prepare(struct drm_gpuva_op_unmap *u)
 	drm_gpuva_unmap(u);
 }
 
+/*
+ * Note: @args should not be NULL when calling for a map operation.
+ */
 static int
 nouveau_uvmm_sm_prepare(struct nouveau_uvmm *uvmm,
 			struct nouveau_uvma_prealloc *new,
@@ -628,7 +631,7 @@ nouveau_uvmm_sm_prepare(struct nouveau_uvmm *uvmm,
 			if (ret)
 				goto unwind;
 
-			if (args && vmm_get_range) {
+			if (vmm_get_range) {
 				ret = nouveau_uvmm_vmm_get(uvmm, vmm_get_start,
 							   vmm_get_range);
 				if (ret) {