ixgbe: fix bit shift overflow in VMDQ pool setup

ixgbe: fix bit shift overflow in VMDQ pool setup

Fix issue reported by Coverity.

Coverity ID 13193: Bad bit shift operation (BAD_SHIFT)
large_shift: In expression 1 << pool, left shifting by more than 31 bits
has undefined behavior. The shift amount, pool, is at least 32.

This patch is a rework of register addr selection logic and mask
computation to made it more readable and avoid bit overflow when 32 bit
value is shifted over its size for pool > 31.

Fixes: fe3a45fd4104 ("ixgbe: add VMDq support")
Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>