drm/vmwgfx: Fix NULL pointer comparison

Replace direct comparisons to NULL i.e.
'x == NULL' with '!x'. As per coding standard.

Signed-off-by: Ravikant B Sharma <ravikant.s2@samsung.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Sinclair Yeh <syeh@vmware.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c b/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
index 941bcfd..b17f08f 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_mob.c
@@ -320,14 +320,14 @@ int vmw_otables_setup(struct vmw_private *dev_priv)
 
 	if (dev_priv->has_dx) {
 		*otables = kmemdup(dx_tables, sizeof(dx_tables), GFP_KERNEL);
-		if (*otables == NULL)
+		if (!(*otables))
 			return -ENOMEM;
 
 		dev_priv->otable_batch.num_otables = ARRAY_SIZE(dx_tables);
 	} else {
 		*otables = kmemdup(pre_dx_tables, sizeof(pre_dx_tables),
 				   GFP_KERNEL);
-		if (*otables == NULL)
+		if (!(*otables))
 			return -ENOMEM;
 
 		dev_priv->otable_batch.num_otables = ARRAY_SIZE(pre_dx_tables);
@@ -407,7 +407,7 @@ struct vmw_mob *vmw_mob_create(unsigned long data_pages)
 {
 	struct vmw_mob *mob = kzalloc(sizeof(*mob), GFP_KERNEL);
 
-	if (unlikely(mob == NULL))
+	if (unlikely(!mob))
 		return NULL;
 
 	mob->num_pages = vmw_mob_calculate_pt_pages(data_pages);