staging: rtl8192e: Rename firmware_check_ready

Use naming schema found in other rtlwifi devices.
Rename firmware_check_ready to _rtl92e_fw_check_ready.

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