mmc: sdhci-bcm-kona: fix build errors when built-in

`sdhci_bcm_kona_remove' referenced in section `.data' of drivers/built-in.o: defined in discarded section `.exit.text' of drivers/built-in.o

Fixes: 058feb53 ("mmc: sdhci-bcm-kona: make linker-section warning go away")
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Mayer <markus.mayer@linaro.org>
Acked-by: Matt Porter <mporter@linaro.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Chris Ball <chris@printf.net>