staging: rtl8192u: Make core functions static

This patch fixes the following sparse warnings in r8192U_core.c:

  CHECK   drivers/staging/rtl8192u/r8192U_core.c
drivers/staging/rtl8192u/r8192U_core.c:3212:6: warning: symbol
'rtl819x_watchdog_wqcallback' was not declared. Should it be static?
drivers/staging/rtl8192u/r8192U_core.c:3276:6: warning: symbol
'watch_dog_timer_callback' was not declared. Should it be static?
drivers/staging/rtl8192u/r8192U_core.c:3282:5: warning: symbol
'_rtl8192_up' was not declared. Should it be static?
drivers/staging/rtl8192u/r8192U_core.c:3333:5: warning: symbol
'rtl8192_close' was not declared. Should it be static?
drivers/staging/rtl8192u/r8192U_core.c:3406:6: warning: symbol
'rtl8192_restart' was not declared. Should it be static?
drivers/staging/rtl8192u/r8192U_core.c:4618:6: warning: symbol
'rtl8192_irq_rx_tasklet' was not declared. Should it be static?
drivers/staging/rtl8192u/r8192U_core.c:4736:6: warning: symbol
'rtl8192_cancel_deferred_work' was not declared. Should it be static?

Signed-off-by: Nickolaus Woodruff <nickolauswoodruff@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>