msdk: fix typo

https://bugzilla.gnome.org/show_bug.cgi?id=794276

sys/msdk/gstmsdksystemmemory.c

diff --git a/sys/msdk/gstmsdksystemmemory.c b/sys/msdk/gstmsdksystemmemory.c
index a7636c5..b813073 100644
--- a/sys/msdk/gstmsdksystemmemory.c
+++ b/sys/msdk/gstmsdksystemmemory.c
@@ -165,7 +165,7 @@
       GST_VIDEO_INFO_SIZE (vip));
 
   if (!ensure_data (mem))
-    return FALSE;
+    return NULL;
 
   return GST_MEMORY_CAST (mem);
 }
@@ -180,13 +180,13 @@
 
   if (!mem->surface) {
     GST_WARNING ("The surface is not allocated");
-    return FALSE;
+    return NULL;
   }
 
   if ((info->flags & GST_MAP_WRITE) && mem->surface
       && mem->surface->Data.Locked) {
     GST_WARNING ("The surface in memory %p is not still avaliable", mem);
-    return FALSE;
+    return NULL;
   }
 
   return mem->surface->Data.Y;

sys/msdk/gstmsdkvideomemory.c

diff --git a/sys/msdk/gstmsdkvideomemory.c b/sys/msdk/gstmsdkvideomemory.c
index ab02ab9..ced7c96 100644
--- a/sys/msdk/gstmsdkvideomemory.c
+++ b/sys/msdk/gstmsdkvideomemory.c
@@ -114,7 +114,7 @@
 
   mem->surface = gst_msdk_video_allocator_get_surface (base_allocator);
   if (!mem->surface)
-    return FALSE;
+    return NULL;
 
   vip = &allocator->image_info;
   gst_memory_init (&mem->parent_instance, GST_MEMORY_FLAG_NO_SHARE,
@@ -228,13 +228,13 @@
 
   if (!mem->surface) {
     GST_WARNING ("The surface is not allocated");
-    return FALSE;
+    return NULL;
   }
 
   if ((info->flags & GST_MAP_WRITE) && mem->surface
       && mem->surface->Data.Locked) {
     GST_WARNING ("The surface in memory %p is not still avaliable", mem);
-    return FALSE;
+    return NULL;
   }
 
   gst_msdk_frame_lock (msdk_video_allocator->context, mem->surface->Data.MemId,