fs/compat_ioctl.c: fix an underflow issue (harmless)

We cap "nmsgs" at I2C_RDRW_IOCTL_MAX_MSGS (42) but the current code
allows negative values.  It's harmless but it makes my static checker
upset so I've made nsmgs unsigned.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/compat_ioctl.c

@@ -680,7 +680,8 @@ static int do_i2c_rdwr_ioctl(unsigned int fd, unsigned int cmd,
 	struct i2c_msg			__user *tmsgs;
 	struct i2c_msg32		__user *umsgs;
 	compat_caddr_t			datap;
-	int				nmsgs, i;
+	u32				nmsgs;
+	int				i;
 
 	if (get_user(nmsgs, &udata->nmsgs))
 		return -EFAULT;