net: stmmac: configure PTP clock source prior to PTP initialization

For Intel platform, it is required to configure PTP clock source prior PTP
initialization in MAC. So, need to move ptp_clk_freq_config execution from
stmmac_ptp_register() to stmmac_init_ptp().

Fixes: 76da35dc

 ("stmmac: intel: Add PSE and PCH PTP clock source selection")
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Mohammad Athari Bin Ismail <mohammad.athari.ismail@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>