i40e: fix potential memory leaks in i40e_remove()

Instead of freeing memory of a single VSI, make sure
the memory for all VSIs is cleared before releasing VSIs.
Add releasing of their resources in a loop with the iteration
number equal to the number of allocated VSIs.

Fixes: 41c445ff ("i40e: main driver core")
Signed-off-by: Andrii Staikov <andrii.staikov@intel.com>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>