mmc: Clean up generic mmc driver multi-block write functions

The current mmc write implementation is type ulong, but returns int values.
Some of the printf's are terminated with /n/r, one has none.

This patch fixes these issues and also removes some unnecessary local
variables.

Signed-off-by: Steve Sakoman <steve.sakoman@linaro.org>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>