CLEANUP: Include check.h in flt_spoe.c

This is required for the prototype of spoe_prepare_healthcheck_request().
diff --git a/src/flt_spoe.c b/src/flt_spoe.c
index f6e14d3..70aa869 100644
--- a/src/flt_spoe.c
+++ b/src/flt_spoe.c
@@ -17,6 +17,7 @@
 #include <haproxy/api.h>
 #include <haproxy/arg.h>
 #include <haproxy/cfgparse.h>
+#include <haproxy/check.h>
 #include <haproxy/filters.h>
 #include <haproxy/freq_ctr.h>
 #include <haproxy/frontend.h>