xdp-tools: fix wrong matching for OPENWRT_VERBOSE

To enable verbose log for xdp-tools compilation, we check for "c" in
the OPENWRT_VERBOSE, but verbose.mk supports only "w" and "s" for V=1
and V=99.

Fix the wrong matching and correctly enable verbose output matching for
"s".

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

package/network/utils/xdp-tools/Makefile

@@ -89,7 +89,7 @@ CONFIGURE_VARS += \
 	LLC="$(LLVM_LLC)" \
 	BPF_LDFLAGS="-march=$(BPF_TARGET) -mcpu=v3"
 
-ifneq ($(findstring c,$(OPENWRT_VERBOSE)),)
+ifneq ($(findstring s,$(OPENWRT_VERBOSE)),)
 	MAKE_FLAGS+=V=1
 endif