Fix Windows x64 build errors with type conversions

Signed-off-by: Agathiyan Bragadeesh <agathiyan.bragadeesh2@arm.com>
diff --git a/library/x509.c b/library/x509.c
index f3f3c87..8145fb8 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -826,9 +826,8 @@
 int mbedtls_x509_dn_gets(char *buf, size_t size, const mbedtls_x509_name *dn)
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    size_t i, j, n, asn1_len_size;
+    size_t i, j, n, asn1_len_size, asn1_len_start;
     unsigned char asn1_len_buf[5];
-    int asn1_len_start;
     unsigned char *asn1_len_p;
     unsigned char c, merge = 0;
     const mbedtls_x509_name *name;