Fix segmentation fault in hbd path

When CONFIG_VP9_HIGHBITDEPTH is enabled,
lowbd modules were called in the hbd path.
This patch fixes the issue.

(cherry picked from commit 797ec1cd66c04fd335adba8ecc01dc93eab1898e)

BUG=webm:1589

Change-Id: I1caf701514dbf80eb75b953f40b1e7238f265a2c
1 file changed