brcmfmac: limit hex dump on fwil.

When debug is turned on for fwil then the whole data buffer is
dumped. In some cases this gives excessive amount of debug. With
this patch the dumps are limited to 64 bytes.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>