bnxt_en: Fix bitmap declaration to work on 32-bit arches.

The declaration of the bitmap vf_req_snif_bmap using fixed array of
unsigned long will only work on 64-bit archs.  Use DECLARE_BITMAP instead
which will work on all archs.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>