mmc: davinci: remove matching string

The string "MMCSDCLK" is not actually used for clock lookup, so can be
removed.

Signed-off-by: David Lechner <david@lechnology.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>