rsi: Changes in USB read and write operations

USB read and write registers maximum size is limited 2^16. More than
this size is not used in the driver.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>