Fix dependency in hls.gyp

Seeing occasional build breaks when building hls_builder, e.g.
https://travis-ci.org/google/shaka-packager/jobs/143445907
Although hls_builder is dependent on widevine_pssh_data_proto
indirectly (through media_base), it does not work all the time.
Looks like the proto has to be a direct dependency.

Change-Id: Id4d9d0b9e669df0967cc767132ef29717243a722

packager/hls/hls.gyp

@@ -24,6 +24,7 @@
       'dependencies': [
         '../base/base.gyp:base',
         '../media/base/media_base.gyp:media_base',
+        '../media/base/media_base.gyp:widevine_pssh_data_proto',
         '../media/file/file.gyp:file',
         '../mpd/mpd.gyp:media_info_proto',
       ],