ASN.1: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

This patch fixes the following warnings:

lib/asn1_decoder.c:386:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
lib/asn1_decoder.c:449:6: warning: this statement may fall through [-Wimplicit-fallthrough=]

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enabling
-Wimplicit-fallthrough.

Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Gustavo A. R. Silva <[email protected]>

lib/asn1_decoder.c

@@ -385,6 +385,8 @@ int asn1_ber_decoder(const struct asn1_decoder *decoder,
 	case ASN1_OP_END_SET_ACT:
 		if (unlikely(!(flags & FLAG_MATCHED)))
 			goto tag_mismatch;
+		/* fall through */
+
 	case ASN1_OP_END_SEQ:
 	case ASN1_OP_END_SET_OF:
 	case ASN1_OP_END_SEQ_OF:
@@ -450,6 +452,8 @@ int asn1_ber_decoder(const struct asn1_decoder *decoder,
 			pc += asn1_op_lengths[op];
 			goto next_op;
 		}
+		/* fall through */
+
 	case ASN1_OP_ACT:
 		ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
 		if (ret < 0)