OMAP: hsmmc: fix memory leak

The platform data allocated with kmalloc() will become unreachable once
the init is complete, so it should be freed. The problem was discovered
by kmemleak.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Acked-by: Adrian Hunter <adrian.hunter@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>