usb: composite: Adjust MaxPower based on enumerated USB speed

USB device is trying to draw 900mA when enumerated in USB high speed
mode although reporting bMaxPower as 500mA to host. Fix this issue by
adjusting MaxPower based on enumerated USB speed before reporting
current to draw to linux charger driver.

Change-Id: I37032c83be6403004ee8d107cb8d7cae04fa0ffa
Signed-off-by: Mayank Rana <mrana@codeaurora.org>