sfc: fix ef100 RX prefix macro

Macro PREFIX_WIDTH_MASK uses unsigned long arithmetic for a shift of up
 to 32 bits, which breaks on 32-bit systems.  This did not previously
 show up as we weren't using any fields of width 32, but we now need to
 access ESF_GZ_RX_PREFIX_USER_MARK.
Change it to unsigned long long.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>