i2c: guarantee that I2C_M_RD will be 0x0001 forever

There is code out there in user space and kernel space which relies on
I2C_M_RD being bit 0 to simplify their bit operations. Add a comment to
make sure this will never break. Do proper sorting of the defines while
we are here.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

include/uapi/linux/i2c.h

@@ -68,14 +68,15 @@
 struct i2c_msg {
 	__u16 addr;	/* slave address			*/
 	__u16 flags;
-#define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
 #define I2C_M_RD		0x0001	/* read data, from slave to master */
-#define I2C_M_STOP		0x8000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-#define I2C_M_NOSTART		0x4000	/* if I2C_FUNC_NOSTART */
-#define I2C_M_REV_DIR_ADDR	0x2000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-#define I2C_M_IGNORE_NAK	0x1000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-#define I2C_M_NO_RD_ACK		0x0800	/* if I2C_FUNC_PROTOCOL_MANGLING */
+					/* I2C_M_RD is guaranteed to be 0x0001! */
+#define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
 #define I2C_M_RECV_LEN		0x0400	/* length will be first received byte */
+#define I2C_M_NO_RD_ACK		0x0800	/* if I2C_FUNC_PROTOCOL_MANGLING */
+#define I2C_M_IGNORE_NAK	0x1000	/* if I2C_FUNC_PROTOCOL_MANGLING */
+#define I2C_M_REV_DIR_ADDR	0x2000	/* if I2C_FUNC_PROTOCOL_MANGLING */
+#define I2C_M_NOSTART		0x4000	/* if I2C_FUNC_NOSTART */
+#define I2C_M_STOP		0x8000	/* if I2C_FUNC_PROTOCOL_MANGLING */
 	__u16 len;		/* msg length				*/
 	__u8 *buf;		/* pointer to msg data			*/
 };