mmc: sdhci-bcm-kona: make linker-section warning go away

This change makes the following build warning go away:
[...]
  LINK    vmlinux
  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: modpost: Found 2 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

Signed-off-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Christian Daudt <csd@broadcom.com>
Reviewed-by: Matt Porter <matt.porter@linaro.org>