mmc: set rca to 1 for MMC cards

U-Boot currently sets MMC cards' RCA register to 0. This value is
reserved according to the specification. Use a value of 1 instead, just
like the Linux kernel.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>