net: fec: Fix possible NPD in fec_enet_phy_reset_after_clk_enable()

The function of_phy_find_device may return NULL, so we need to take
care before dereferencing phy_dev.

Fixes: 64a632da ("net: fec: Fix phy_device lookup for phy_reset_after_clk_enable()")
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Cc: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: Richard Leitner <richard.leitner@skidata.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Wei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20250904091334.53965-1-wahrenst@gmx.net


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