phy: usb: bdc: Fix occasional failure with BDC on 7211

The BDC "Read Transaction Size" needs to be changed from 1024
bytes to 256 bytes to prevent occasional transaction failures.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>