mmc: matsushita-common: Handle bus width 0

Handle bus width 0 as 1-bit bus to assure valid content of
MATSU_SD_OPTION register WIDTH field.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>