USB: Align buffers at cacheline

This avoids cache-alignment warnings shown in console
when a usb command is entered.

Whenever X bytes of unaligned buffer is invalidated, arm core
invalidates X + Y bytes as per the cache line size and throws
these warnings.

Signed-off-by: Puneet Saxena <puneets@nvidia.com>
Signed-off-by: Marek Vasut <marex@denx.de>