ixgbe: remove redundant initialization of 'pool'

Variable pool is being assigned zero and then in the following for-loop
is it being set to zero again. Remove the redundant first assignment.

Cleans up clang warning:
drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c:61:2: warning: Value stored
to 'pool' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>