lavfi/drawutils: fix typo

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/drawutils.h

@@ -51,8 +51,8 @@ typedef struct FFDrawContext {
     unsigned nb_planes;
     int pixelstep[MAX_PLANES]; /*< offset between pixels */
     uint8_t comp_mask[MAX_PLANES]; /*< bitmask of used non-alpha components */
-    uint8_t hsub[MAX_PLANES];  /*< horizontal subsamling */
-    uint8_t vsub[MAX_PLANES];  /*< vertical subsamling */
+    uint8_t hsub[MAX_PLANES];  /*< horizontal subsampling */
+    uint8_t vsub[MAX_PLANES];  /*< vertical subsampling */
     uint8_t hsub_max;
     uint8_t vsub_max;
 } FFDrawContext;