leds: blinkm: Fix CONFIG_LEDS_CLASS_MULTICOLOR dependency

With CONFIG_LEDS_CLASS_MULTICOLOR=m, a builtin leds-blinkm driver causes
a link failure:

arm-linux-gnueabi-ld: drivers/leds/leds-blinkm.o: in function `blinkm_set_mc_brightness':
leds-blinkm.c:(.text.blinkm_set_mc_brightness+0xc): undefined reference to `led_mc_calc_color_components'

Add a more specific dependency that only allows multicoler mode to
be enabled for blinkm if it can build and link.

Fixes: 56e8c56c9af0 ("leds: Add multicolor support to BlinkM LED driver")
Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: Joseph Strauss <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/Kconfig

···
 config LEDS_BLINKM_MULTICOLOR
 	bool "Enable multicolor support for BlinkM I2C RGB LED"
 	depends on LEDS_BLINKM
-	depends on LEDS_CLASS_MULTICOLOR
+	depends on LEDS_CLASS_MULTICOLOR=y || LEDS_CLASS_MULTICOLOR=LEDS_BLINKM
 	help
 	  This option enables multicolor sysfs class support for BlinkM LED and
 	  disables the older, separated sysfs interface