net: brcm80211: Deletion of unnecessary checks before two function calls

The functions brcmu_pkt_buf_free_skb() and release_firmware() test whether
their argument is NULL and then return immediately. Thus the test around
the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>