avcodec/libx264: fix usage of AVComponentDescriptor depth field

AVComponentDescriptor.depth is not available in release/2.4

This fixes compilation of the libx264 wrapper.

Signed-off-by: James Almer <jamrial@gmail.com>
diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
index 72427d3..97fc62f 100644
--- a/libavcodec/libx264.c
+++ b/libavcodec/libx264.c
@@ -398,7 +398,7 @@
     x4->params.i_log_level          = X264_LOG_DEBUG;
     x4->params.i_csp                = convert_pix_fmt(avctx->pix_fmt);
 #if X264_BUILD >= 153
-    x4->params.i_bitdepth           = av_pix_fmt_desc_get(avctx->pix_fmt)->comp[0].depth;
+    x4->params.i_bitdepth           = av_pix_fmt_desc_get(avctx->pix_fmt)->comp[0].depth_minus1 + 1;
 #endif
 
     OPT_STR("weightp", x4->wpredp);