ixgbe: ptp code cleanup

This patch fixes two minor nits from Richard Cochran. The first is a case of
ambitious line wrapping that wasn't necessary. The second is to re-order the
flag checks for PPS support. Previously, the hardware test was done first, and
the interrupt flag test was done second. Now, test the interrupt flag and use
the unlikely macro.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>