usb: dwc2: Align size of invalidating dcache before starting DMA

During using dwc2 usb gadget, if usb message size is too small,
following cache misaligned warning is shown:

   CACHE: Misaligned operation at range [bfdbcb00, bfdbcb04]

Align size of invalidating dcache before starting DMA to remove the
warning.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>