core: ltc: SM2 DSA: fix configuration variable name

The name of the config variable indicating support for SM2 DSA is
_CFG_CORE_LTC_SM2_DSA, not _CFG_CORE_LTC_SM2_DSA_SM3.

Fixes: 76c7ba4b9ff7 ("core: ltc: add support for SM2 DSA")
Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/core/lib/libtomcrypt/sub.mk b/core/lib/libtomcrypt/sub.mk
index 47543b1..6a841c2 100644
--- a/core/lib/libtomcrypt/sub.mk
+++ b/core/lib/libtomcrypt/sub.mk
@@ -107,7 +107,7 @@
    # ECC 521 bits is the max supported key size
    cppflags-lib-y += -DLTC_MAX_ECC=521
 endif
-ifeq ($(filter y,$(_CFG_CORE_LTC_SM2_DSA_SM3) $(_CFG_CORE_LTC_SM2_PKE)),y)
+ifneq (,$(filter y,$(_CFG_CORE_LTC_SM2_DSA) $(_CFG_CORE_LTC_SM2_PKE)))
    cppflags-lib-y += -DLTC_ECC_SM2
 endif