usb: phy: generic: Convert to devm_clk_get_optional()

usb: phy: generic: Convert to devm_clk_get_optional()

The generic USB PHY driver uses the existence of the "clocks" property
to see if a clock is optional or not.  Use devm_clk_get_optional()
instead, which exists for this purpose.  As usb_phy_generic.clk is now
either a valid clock pointer or NULL, and all clock operations handle
NULL pointers gracefully, several IS_ERR() checks can be removed,
simplifying the code.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
...

Link: https://patch.msgid.link/5cc21d821edf5d40f56a74cd251bb1b982876b72.1769004444.git.geert+renesas@glider.be
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>