staging: brcm80211: fix potential null pointer access handling ucode buffer

Allocation of buffer in function wl_ucode_init_buf can fail. This was
signalled by an error message, but code continued to access the null
pointer. This is now avoided by jumping to failure label.

Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Brett Rudley <brudley@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>