Correct a default value

Per comment in the codebase, force_video_mode by default should be 0,
i.e. disabled. This commit correct the value in default config to be
consistent.

BUG=aomedia:2577

Change-Id: I4c5e3bcf221b31c6d8d33d3a945a88d6e0a6cf13
diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index d3cba5e..0930b72 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -180,7 +180,7 @@
   0,                                         // lossless
   1,                                         // enable_cdef
   1,                                         // enable_restoration
-  1,                                         // force_video_mode
+  0,                                         // force_video_mode
   1,                                         // enable_obmc
   3,                                         // disable_trellis_quant
   0,                                         // enable_qm