fix -Wmaybe-uninitialized compile warning in nist-sts

fix compile warning as following:
nist-sts/sts/src/cusum.c:15:23: warning: 'zerv' may be used uninitialized in this function[-Werror=maybe-uninitialized]

Signed-off-by: makejian <makejian@xiaomi.com>
diff --git a/testing/nist-sts/Makefile b/testing/nist-sts/Makefile
index d4dd405..771c1ad 100644
--- a/testing/nist-sts/Makefile
+++ b/testing/nist-sts/Makefile
@@ -49,7 +49,8 @@
 MAINSRC   = nist-sts/sts/src/assess.c
 CSRCS     = $(shell find nist-sts/sts/src -name "*.c" ! -name "assess.c")
 CFLAGS   += -Wno-misleading-indentation -Wno-unused-but-set-variable \
-            -Wno-strict-prototypes -Wno-undef -Wno-shadow -Wno-unused-variable
+            -Wno-strict-prototypes -Wno-undef -Wno-shadow -Wno-unused-variable \
+            -Wno-maybe-uninitialized
 
 # Download and unpack tarball if no git repo found
 ifeq ($(wildcard $(NIST_UNPACKNAME)/.git),)