target: remove more exit() calls

These were all basically "can't happen" cases ... like having
state be corrupted by an alpha particle after the previous check
for whether a value was in-range.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/target.c

@@ -2154,8 +2154,9 @@ static void handle_md_output(struct command_context *cmd_ctx,
 	case 2: value_fmt = "%4.2x "; break;
 	case 1: value_fmt = "%2.2x "; break;
 	default:
+		/* "can't happen", caller checked */
 		LOG_ERROR("invalid memory read size: %u", size);
-		exit(-1);
+		return;
 	}
 
 	for (unsigned i = 0; i < count; i++)