Device connected to MMC3 is assumed to be self-powered, so
set_power() function is empty. It can't be omited because
host driver requires it.

Array size for hsmmc[] is specified to allocate to allocate
an instance for the third MMC controller.

Also fix a leak which happens if invalid controller id
is passed.
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>