printk: silence healthd messages from userspace

Constant messages about battery status every second doesn't help battery
or debugging.

Signed-off-by: kdrag0n <dragon@khronodragon.com>

kernel/printk/printk.c

@@ -802,6 +802,10 @@ static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 		}
 	}
 
+	if (strncmp("healthd", line, 7) == 0) {
+		return len;
+	}
+
 	printk_emit(facility, level, NULL, 0, "%s", line);
 	kfree(buf);
 	return ret;