mmc: sanitize 'bus width' in debug output

The bus width is sometimes the actual bus width, and sometimes indices
to different arrays encoding the bus width. In my debugging case "2"
could mean 8-bit as well as 4-bit, which was extremly confusing. Let's
use the human-readable actual bus width in all places.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>