Fix all sign/unsigned warnings with Clang and GCC.

Change-Id: If2a83698236f7b0dcd46701ccd257a85463d6ce5
Reviewed-on: https://boringssl-review.googlesource.com/4992
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/ssl_asn1.c b/ssl/ssl_asn1.c
index 9e61fb6..0ad4a11 100644
--- a/ssl/ssl_asn1.c
+++ b/ssl/ssl_asn1.c
@@ -130,7 +130,7 @@
  *     compressionMethod       [11] OCTET STRING OPTIONAL,
  *     srpUsername             [12] OCTET STRING OPTIONAL, */
 
-static const int kVersion = 1;
+static const unsigned kVersion = 1;
 
 static const int kTimeTag =
     CBS_ASN1_CONSTRUCTED | CBS_ASN1_CONTEXT_SPECIFIC | 1;