ixgbe: fix missing function pointer conversion

In the previous commit:
  commit 5e655105
  Author: Don Skidmore <donald.c.skidmore@intel.com>
  Date:   Fri Feb 25 01:58:04 2011 +0000

  ixgbe: add function pointer for semaphore function

there was one release of the semaphore function call which
did not get converted to a function pointer.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>