Correctly handle the return value from EVP_Cipher() in the CMAC code

EVP_Cipher() is a very low level routine that directly calls the
underlying cipher function. It's return value semantics are very odd.
Depending on the type of cipher 0 or -1 is returned on error. We should
just check for <=0 for a failure.

Fixes #11957

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11972)

crypto/cmac/cmac.c

@@ -145,7 +145,7 @@ int CMAC_Init(CMAC_CTX *ctx, const void *key, size_t keylen,
             return 0;
         if ((bl = EVP_CIPHER_CTX_block_size(ctx->cctx)) < 0)
             return 0;
-        if (!EVP_Cipher(ctx->cctx, ctx->tbl, zero_iv, bl))
+        if (EVP_Cipher(ctx->cctx, ctx->tbl, zero_iv, bl) <= 0)
             return 0;
         make_kn(ctx->k1, ctx->tbl, bl);
         make_kn(ctx->k2, ctx->k1, bl);
@@ -186,12 +186,12 @@ int CMAC_Update(CMAC_CTX *ctx, const void *in, size_t dlen)
             return 1;
         data += nleft;
         /* Else not final block so encrypt it */
-        if (!EVP_Cipher(ctx->cctx, ctx->tbl, ctx->last_block, bl))
+        if (EVP_Cipher(ctx->cctx, ctx->tbl, ctx->last_block, bl) <= 0)
             return 0;
     }
     /* Encrypt all but one of the complete blocks left */
     while (dlen > (size_t)bl) {
-        if (!EVP_Cipher(ctx->cctx, ctx->tbl, data, bl))
+        if (EVP_Cipher(ctx->cctx, ctx->tbl, data, bl) <= 0)
             return 0;
         dlen -= bl;
         data += bl;