Fix pkg-config file to avoid overlinking

Libraries that are used internally by opusfile but are not part of
 its API should be listed in pkg-config "private" clauses.
Otherwise executables that are linked dynamically against opusfile
 will have unneeded direct dependencies (overlinking).

Signed-off-by: Timothy B. Terriberry <tterribe@xiph.org>

opusfile.pc.in

@@ -8,7 +8,7 @@ includedir=@includedir@
 Name: opusfile
 Description: High-level Opus decoding library
 Version: @VERSION@
-Requires: ogg >= 1.3 opus >= 1.0.1 @openssl@
+Requires.private: ogg >= 1.3 opus >= 1.0.1 @openssl@
 Conflicts:
 Libs: -L${libdir} -lopusfile
 Libs.private: @lrintf_lib@