ixgbe: Correct X540 semaphore error

In the function ixgbe_get_swfw_sync_semaphore, an incorrect
check was treating success as failure and vice-versa. This led
to manipulating the IXGBE_SWFW_SYNC register without holding
the software semaphore first, which is an error. In addition,
if getting the REGSMP bit in the IXGBE_SW_FW_SYNC register
timed out, no error code would be returned, making the caller
think that it had successfully acquired the lock. Fix both of
those issues and clean up the function a bit, such as make the
name in the comment match the function.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>