The sd host controller spec indicates the the MAX_CURRENT value may
be returned as 0.  In this case other methods need to be used to
return the current.  If 0 is returned and there is a regulator,
ask the regulator for how much current is available.
Signed-off-by: NPhilip Rakity <prakity@marvell.com>
Signed-off-by: NMark F. Brown <mark.brown314@gmail.com>
Reviewed-by: NAaron Lu <aaron.lu@amd.com>
Signed-off-by: NChris Ball <cjb@laptop.org>