ice: fix stack leakage

In the case of an invalid virtchannel request the driver
would return uninitialized data to the VF from the PF stack
which is a bug.  Fix by initializing the stack variable
earlier in the function before any return paths can be taken.

Fixes: 1071a835 ("ice: Implement virtchnl commands for AVF support")
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>