net: ti: icssg_prueth: Fix NULL pointer dereference in prueth_probe()

In the prueth_probe() function, if one of the calls to emac_phy_connect()
fails due to of_phy_connect() returning NULL, then the subsequent call to
phy_attached_info() will dereference a NULL pointer.

Check the return code of emac_phy_connect and fail cleanly if there is an
error.

Fixes: 128d5874

 ("net: ti: icssg-prueth: Add ICSSG ethernet driver")
Cc: stable@vger.kernel.org
Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://lore.kernel.org/r/20240521-icssg-prueth-fix-v1-1-b4b17b1433e9@bootlin.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>