mmc: sdhci-{pxav2,pxav3}: Use of_match_ptr() macro

This eliminates having an #ifdef returning NULL for the case
when OF is disabled.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>