mmc: renesas_sdhi_internal_dmac: Fix a few typos

Remove the stray underscore in the DM_CM_DTRAN_MODE.BUS_WIDTH register
field name and fix the typo in the comment of the #define
DTRAN_MODE_CH_NUM_CH1.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>