package/xerces: fix coding style in Config.in

We generally use on "depends on" for each toolchain option, so let's
do this as well in package/xerces/Config.in.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/xerces/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_XERCES
 	bool "xerces-c++"
-	depends on BR2_INSTALL_LIBSTDCPP && BR2_USE_WCHAR
+	depends on BR2_INSTALL_LIBSTDCPP
+	depends on USE_WCHAR
 	help
 	  Xerces-C++ is a validating XML parser written in portable C++.