brcmfmac: Delete redundant length check

brcmf_fweh_process_event() sets event->datalen to the
endian-swapped value of event_packet->msg.datalen, which is the
same as emsg.datalen.  This length is already validated in
brcmf_fweh_process_event(), so there is no need to check it
again upon dequeuing the event.

Suggested-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kevin Cernekee <cernekee@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>