ixgbe: return early instead of wrap block in if statement

Since we exit at the end of the block, we can save a level of
indentation by performing an early return, and make the next several
sections of code more legible, with fewer 80 character line breaks.

Also moved allocating vfinfo at the beginning and the notification
for enabling SRIOV at the end of the function when we know that it
will succeed.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>