BUG FIX: undefined reference to `vp9_scale_and_extend_frame_c'

See https://bugs.chromium.org/p/webm/issues/detail?id=1145

Change-Id: I778ee07dc39a524e3f729bef47a7abeed51e0cee

vp9/vp9cx.mk

diff --git a/vp9/vp9cx.mk b/vp9/vp9cx.mk
index 83a91e8..2930c23 100644
--- a/vp9/vp9cx.mk
+++ b/vp9/vp9cx.mk
@@ -119,7 +119,9 @@
 
 VP9_CX_SRCS-$(HAVE_SSE2) += encoder/x86/vp9_dct_sse2.c
 VP9_CX_SRCS-$(HAVE_SSSE3) += encoder/x86/vp9_dct_ssse3.c
+ifneq ($(CONFIG_VP9_HIGHBITDEPTH),yes)
 VP9_CX_SRCS-$(HAVE_SSSE3) += encoder/x86/vp9_frame_scale_ssse3.c
+endif
 
 ifeq ($(CONFIG_VP9_TEMPORAL_DENOISING),yes)
 VP9_CX_SRCS-$(HAVE_SSE2) += encoder/x86/vp9_denoiser_sse2.c