Only propagate register errors on some targets

Without this change, connecting to ARM targets is impossible.

Fixes #115.

Change-Id: Ie33c7e15ac1bed8c9cbd8e6a78de92d5498c5999

src/target/riscv/riscv.c

@@ -245,6 +245,7 @@ static int riscv_init_target(struct command_context *cmd_ctx,
 		struct target *target)
 {
 	LOG_DEBUG("riscv_init_target()");
+	target->propagate_register_errors = true;
 	target->arch_info = calloc(1, sizeof(riscv_info_t));
 	if (!target->arch_info)
 		return ERROR_FAIL;