usb: core: Remove redundant vmap checks

Now that the vmap area checks are being performed in the DMA
infrastructure directly, there is no need to repeat them in USB.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>