ptp: ptp_clockmatrix: Fix build error

When do randbuilding, we got this warning:

WARNING: unmet direct dependencies detected for PTP_1588_CLOCK
  Depends on [n]: NET [=y] && POSIX_TIMERS [=n]
  Selected by [y]:
  - PTP_1588_CLOCK_IDTCM [=y]

Make PTP_1588_CLOCK_IDTCM depends on PTP_1588_CLOCK to fix this.

Fixes: 3a6ba7d ("ptp: Add a ptp clock driver for IDT ClockMatrix.")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Vincent Cheng  <vincent.cheng.xh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/Kconfig

@@ -121,7 +121,7 @@ config PTP_1588_CLOCK_KVM
 
 config PTP_1588_CLOCK_IDTCM
 	tristate "IDT CLOCKMATRIX as PTP clock"
-	select PTP_1588_CLOCK
+	depends on PTP_1588_CLOCK
 	default n
 	help
 	  This driver adds support for using IDT CLOCKMATRIX(TM) as a PTP