staging: rtl8192u: make in r819xU_cmdpkt.c some local functions static

Make some local functions static.

Fix sparse warnings in r819xU_cmdpkt.c

drivers/staging/rtl8192u/r819xU_cmdpkt.c:185:6: warning: symbol 'cmdpkt_beacontimerinterrupt_819xusb' was not declared. Should it be static?

Signed-off-by: Ana Rey <anarey@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>