greybus: simple fixes

A few silly little fixes.
    - Clear out some unnecessary #includes in "debugfs.c"
    - Drop some unneeded parentheses in hd_to_es1()
    - Use &hd->hd_priv in hd_to_es1() to emphasize we are working
      with an embedded array, not a pointer
    - Fix a comment in the header for ap_probe()
    - Drop a duplicate #include in "gpio-gb.c"
    - Fix a use-before-set problem in set_serial_info()

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>