brcmfmac: fix memory leakage in msgbuf

brcmfmac: fix memory leakage in msgbuf

The kbuild robot came up with the following warning:

tree:   .../kernel/git/linville/wireless-next.git master
head:   f79055d98c7246b67eeb02c0fe81dd9ba02fb46d
commit: 985833de382d770edb6e7430644e0c7bfd3750b7
	 [5/13] brcmfmac: Adding msgbuf protocol.

coccinelle warnings:
 drivers/net/wireless/brcm80211/brcmfmac/msgbuf.c:1309:1-28:
   alloc with no test, possible model on line 1318

Looking into the issue, it turned out that the referred allocation
buffer was not being released in failure path nor upon module
unload.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>