Correct pkg-config file for overlinking.

Index: theora.pc.in
--- theora.pc.in.orig
+++ theora.pc.in
@@ -8,7 +8,7 @@ includedir=@includedir@
 Name: theora
 Description: Theora video codec
 Version: @VERSION@
-Requires: ogg >= 1.1
+Requires.private: ogg >= 1.1
 Conflicts:
 Libs: -L${libdir} -ltheora
 Cflags: -I${includedir}