rtlwifi: rtl8192cu: Change firmware upload to use block writes

Driver rtl8192cu writes the firmware with 32-bit asynchronous writes. This
design is OK for USB 2.0 adapters, but the current implementation of
xhcu-hcd has a limited ring size, which is exceeded. By converting to
synchronous block writes, this error is avoided.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>