mmc: core: UHS sdio card that fails should not exceed 50MHz

A UHS sdio card that fails initialization at 1.8v signaling is not in
UHS mode.  We cannot use the speed in the the cis to reflect the bus
speed as this is the maxiumum value and will not reflect the fact
that the host is operating at a lower (non uhs) bus speed.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Reviewed-by: Aaron Lu <aaron.lu@amd.com>
Signed-off-by: Chris Ball <cjb@laptop.org>