mmc: omap_hsmmc: context save after enabling runtime pm

Call context save api after enabling runtime pm to make sure that
register access in context save api happens with clk enabled.

Signed-off-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Venkatraman S <svenkatr@ti.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>