mmc:fix: Set mmc width according to MMC host capabilities

This patch sets the MMC width according to the MMC host capabilities.
It turned out, that there are some targets (e.g. GONI), which are able
to read data from SPI only at 4 bit mode.
This patch restricts the width number according to the MMC host.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Andy Fleming <afleming@gmail.com>