net: bcmasp: fix double disable of clk

Switch to devm_clk_get_optional() so we can manage the clock ourselves.
We dynamically control the clocks depending on the state of the interface
for power savings. The default state is clock disabled, so unbinding the
driver causes a double disable.

Fixes: 490cb412007d ("net: bcmasp: Add support for ASP2.0 Ethernet controller")
Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20260319234813.1937315-3-justin.chen@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>