drivers: usb: mcux: Fix the write operation

1. Do not copy over the data to the local buffer,
it can be directly sent to the controller. The
cache is flushed before calling the HAL send
function. Also do not allocate a buffer from
the heap pool for the write operation.
2. Remove a length check as this is handled by
the HAL driver.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>