MAINTAINERS: Update gianfar_ptp after renaming

Commit ec21e2ec ("freescale: Move the Freescale drivers") moved the
files, update the pattern.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>