i2c: dev: fix potential memory leak in i2cdev_ioctl_rdwr

If I2C_M_RECV_LEN check failed, msgs[i].buf allocated by memdup_user
will not be freed. Pump index up so it will be freed.

Fixes: 838bfa60 ("i2c-dev: Add support for I2C_M_RECV_LEN")
Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>