libp11: include also p11_err.h when InstallDev

Fix the following compilation error

    In file included from openconnect-internal.h:95:0,
		     from ssl.c:41:
    /home/yousong/git-repo/lede-project/lede/staging_dir/target-mips_24kc_musl/usr/include/libp11.h: At top level:
    /home/yousong/git-repo/lede-project/lede/staging_dir/target-mips_24kc_musl/usr/include/libp11.h:27:21: fatal error: p11_err.h: No such file or directory
    compilation terminated.
    make[5]: *** [libopenconnect_la-ssl.lo] Error 1

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

libs/libp11/Makefile

@@ -42,7 +42,7 @@ CONFIGURE_ARGS += --with-enginesdir=/usr/lib/engines
 
 define Build/InstallDev
 	$(INSTALL_DIR) $(1)/usr/include/
-	$(CP) $(PKG_INSTALL_DIR)/usr/include/libp11.h $(1)/usr/include/
+	$(CP) $(PKG_INSTALL_DIR)/usr/include/*.h $(1)/usr/include/
 	$(INSTALL_DIR) $(1)/usr/lib
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libp11.{a,so} $(1)/usr/lib/
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libp11.so* $(1)/usr/lib/