ixgbevf: Do not rewind the Rx ring before bumping tail

The driver is going back one step from its' previous location before
bumping tail. This is incorrect.  We should just be writing the value of
next_to_use into the tail register.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>