net: ixgbevf: Remove redundant initialization of variable ret_val

The variable ret_val is being initialized with a value that is never
read, it is being updated later on. The assignment is redundant and
can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>