mmc: omap_hsmmc: fix request done for sbc error case

mrq is not populated for set block count(cmd23) command.
Use block read/write mmc_commond pointer for request done and
avoid NULL pointer access in error case for sbc (cmd23).

Signed-off-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Chris Ball <chris@printf.net>