mmc: dw_mmc: rockchip: unset the MMC_CAP_ERASE flag

In dw_mmc.c, it's enabled by default.
It doesn't need to set MMC_CAP_ERASE in rockchip anymore.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>