net: fec: Move `fec_ptp_read()` to the top of the file

net: fec: Move `fec_ptp_read()` to the top of the file

This function is used in `fec_ptp_enable_pps()` through
struct cyclecounter read(). Moving the declaration makes
it clearer, what's happening.

Suggested-by: Frank Li <Frank.li@nxp.com>
Link: https://lore.kernel.org/netdev/20240805144754.2384663-1-csokas.bence@prolan.hu/T/#ma6c21ad264016c24612048b1483769eaff8cdf20
Signed-off-by: Csókás, Bence <csokas.bence@prolan.hu>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20240812094713.2883476-1-csokas.bence@prolan.hu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>