net: ftgmac100: refactor getting phy device handle

Consolidate the handling of dedicated PHY and fixed-link phy by taking
advantage of logic in of_phy_get_and_connect() which handles both of
these cases, rather than open coding the same logic in ftgmac100_probe().

Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241022084214.1261174-1-jacky_chou@aspeedtech.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>