staging: rtl8192e: rtl_core: Make functions static

Make as many functions as possible static in rtl_core.c.
If needed - move fw declaration from header.

The following functions were affected:
- rtl8192_is_tx_queue_empty
- rtl819x_watchdog_wqcallback
- watch_dog_timer_callback
- rtl8192_data_hard_stop
- rtl8192_data_hard_resume
- rtl8192_hard_data_xmit
- rtl8192_hard_start_xmit
- rtl8192_tx_cmd
- rtl8192_tx
- rtl8192_pci_initdescring
- rtl8192_irq_tx_tasklet
- rtl8192_irq_rx_tasklet
- rtl8192_cancel_deferred_work
- _rtl8192_up
- rtl8192_up
- rtl8192_down
- rtl8192_restart
- rtl8192_update_cap

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