brcmfmac: allow firmware-signal tlv to be longer than specified

The firmware-signal API specification defines length for the different
tlv. During testing on different devices it turned out not all firmware
used the tlv length according specification. Therefore the length check
is made less strict with this patch.

Reviewed-by: Hante Meuleman <meuleman@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>