Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/include/uapi/linux/mmc/ioctl.h b/include/uapi/linux/mmc/ioctl.h
index 45f369d..00c0812 100644
--- a/include/uapi/linux/mmc/ioctl.h
+++ b/include/uapi/linux/mmc/ioctl.h
@@ -5,7 +5,10 @@
 #include <linux/types.h>
 
 struct mmc_ioc_cmd {
-	/* Implies direction of data.  true = write, false = read */
+	/*
+	 * Direction of data: nonzero = write, zero = read.
+	 * Bit 31 selects 'Reliable Write' for RPMB.
+	 */
 	int write_flag;
 
 	/* Application-specific command.  true = precede with CMD55 */