package/python3: fix unsafe openssl header path

Explicitely set the openssl path so that python3 doesn't search host
header paths for target openssl headers.

Fixes:
 - http://autobuild.buildroot.net/results/c27/c27fe795e079350dd1c9af45be417d41b55e57c3

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/python3/python3.mk

@@ -103,6 +103,7 @@ endif
 
 ifeq ($(BR2_PACKAGE_PYTHON3_SSL),y)
 PYTHON3_DEPENDENCIES += openssl
+PYTHON3_CONF_OPTS += --with-openssl=$(STAGING_DIR)/usr
 else
 PYTHON3_CONF_OPTS += --disable-openssl
 endif