nghttp2: deduplicate files in staging_dir

'38b22b1e: deduplicate files in libnghttp2' missed duplicates in
staging_dir by Build/InstallDev.

Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>
(cherry picked from commit ee1a78331462d0c2394c0e6805e4d12fbfa4882d)

package/libs/nghttp2/Makefile

@@ -35,7 +35,7 @@ define Build/InstallDev
 	$(INSTALL_DATA) $(PKG_INSTALL_DIR)/usr/include/nghttp2/*.h $(1)/usr/include/nghttp2/
 	$(INSTALL_DIR) $(1)/usr/lib/pkgconfig
 	$(INSTALL_DATA) $(PKG_INSTALL_DIR)/usr/lib/pkgconfig/*.pc $(1)/usr/lib/pkgconfig/
-	$(INSTALL_DATA) $(PKG_INSTALL_DIR)/usr/lib/libnghttp2.so* $(1)/usr/lib/
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libnghttp2.so* $(1)/usr/lib/
 endef
 
 define Package/libnghttp2/install