staging: rtl8192e: Simplify rtllib_process_probe_response()

- Extract frame_ctl once and use it as variable.
- Drop endian conversion in is_beacon() function
  (used in simplified function only)
- Simplify debug messages
- Invert STYPE checks in debug messages - it is valid
  as only BEACON and PROBE_RESP are allowed

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