Libertas: fix buffer overflow in lbs_get_essid()

The libertas driver copies the SSID buffer back to the wireless core and
appends a trailing NULL character for termination. This is

a) unnecessary because the buffer is allocated with kzalloc and is hence
   already NULLed when this function is called, and

b) for priv->curbssparams.ssid_len == 32, it writes back one byte too
   much which causes memory corruptions.

Fix this by removing the extra write.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Maithili Hinge <maithili@marvell.com>
Cc: Kiran Divekar <dkiran@marvell.com>
Cc: Michael Hirsch <m.hirsch@raumfeld.com>
Cc: netdev@vger.kernel.org
Cc: libertas-dev@lists.infradead.org
Cc: linux-wireless@lists.infradead.org
Cc: stable@kernel.org
Acked-by: Holger Schurig <holgerschurig@gmail.com>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>