mmc: omap3: fix block read function

mmc: omap3: fix block read function

The OMAP3 block read function is not following API and always returning
1 instead of read block count, fix it. Also to simplify code, merge it
with with a helper function, which was only called from the block read
function.

After this patch ext2 filesystem can be used properly.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>