net: mv643xx: fix wrong devm_clk_get usage

This clock should be optional. In addition, PTR_ERR can be -EPROBE_DEFER
in which case it should return.

devm_clk_get_optional_enabled also allows removing explicit clock enable
and disable calls.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20240930202951.297737-3-rosenp@gmail.com


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