The current code will gets the clock frequency which is used by
gpmi_nfc_compute_hardware_timing(). It makes the code a little mess.

So move the `get clock frequency` code to the
gpmi_nfc_compute_hardware_timing() itself. This makes the code tidy
and clean.

This patch also uses the macro NSEC_PER_SEC to replace the `1000000000`.
Signed-off-by: NHuang Shijie <b32955@freescale.com>
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>