mmc: sdhci: only set 200mA support for 1.8v if 200mA is available

max_current_caps can return 0 if not available from the sd controller.
If no regulator is present or the regulator specifies a current
less then 200ma, we no longer still set the 200mA caps bit anyway.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Reviewed-by: Aaron Lu <aaron_lu@amd.com>
Signed-off-by: Chris Ball <cjb@laptop.org>