Fix install with shared libs on weird systems

Originally committed as revision 22246 to svn://svn.ffmpeg.org/ffmpeg/trunk

subdir.mak

@@ -70,7 +70,7 @@ install-lib$(NAME)-shared: $(SUBDIR)$(SLIBNAME)
 		$(LN_S) $(SLIBNAME_WITH_VERSION) $(SLIBNAME_WITH_MAJOR)
 	$(Q)cd "$(SHLIBDIR)" && \
 		$(LN_S) $(SLIBNAME_WITH_VERSION) $(SLIBNAME)
-	$$(SLIB_INSTALL_EXTRA_CMD)
+	$(SLIB_INSTALL_EXTRA_CMD)
 
 install-lib$(NAME)-static: MSG = $(LIBDIR)/$(LIBNAME)
 install-lib$(NAME)-shared: MSG = $(LIBDIR)/$(SLIBNAME)