leds: as3668: Fix Kconfig symbol name mismatch in Makefile

leds: as3668: Fix Kconfig symbol name mismatch in Makefile

kconfiglint reports:

  X001: CONFIG_LEDS_AS3668 referenced in Makefile but not defined
        in any Kconfig

The AS3668 LED driver was introduced in
commit c7dd343a3756 ("leds:
as3668: Driver for the ams Osram 4-channel i2c LED driver").
That commit defined the Kconfig symbol as LEDS_OSRAM_AMS_AS3668 in
drivers/leds/Kconfig but used the shorter name LEDS_AS3668 in the
Makefile's obj-* line.

Because the Makefile references CONFIG_LEDS_AS3668 which does not exist,
the driver can never be built — the obj-* line always evaluates to
obj- += leds-as3668.o (empty config), so the object file is never
compiled regardless of what the user selects in menuconfig.

Fix the Makefile to reference the correct Kconfig symbol
CONFIG_LEDS_OSRAM_AMS_AS3668, matching what is defined in
drivers/leds/Kconfig.

Assisted-by: Claude:claude-opus-4-6 kconfiglint
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Lukas Timmermann <linux@timmermann.space>
Link: https://patch.msgid.link/20260426000322.55999-1-sashal@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>