staging: rtl8192e: Rename write_nic_byte

Use naming schema found in other rtlwifi devices.
Rename write_nic_byte to rtl92e_writeb.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>