[zephyr] Fix realtime clock (#18470)
[zephyr] Fix realtime clock (#18470)

I applied a code review comment only partially and forgot
to remove the multiplication.
nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,project-chip/connectedhomeip