sfc: fix ef100 design-param checking

The handling of the RXQ/TXQ size granularity design-params had two
 problems: it had a 64-bit divide that didn't build on 32-bit platforms,
 and it could divide by zero if the NIC supplied 0 as the value of the
 design-param.  Fix both by checking for 0 and for a granularity bigger
 than our min-size; if the granularity <= EFX_MIN_DMAQ_SIZE then it fits
 in 32 bits, so we can cast it to u32 for the divide.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Edward Cree <ecree@solarflare.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>