wl12xx: fix sparse warning about undeclared wl12xx_alloc_dummy_packet

Fix sparse warning:

  CHECK   drivers/net/wireless/wl12xx/main.c
drivers/net/wireless/wl12xx/main.c:1246:17: warning: symbol 'wl12xx_alloc_dummy_packet' was not declared. Should it be static?

Signed-off-by: Luciano Coelho <coelho@ti.com>
1 file changed