mmc: davinci_mmc: Prevent transmitted data size from exceeding sgm's length

No check is done on the size of the data to be transmiited. This causes
a kernel panic when this size exceeds the sg_miter's length.

Limit the number of transmitted bytes to sgm->length.

Cc: stable@vger.kernel.org
Fixes: ed01d210

 ("mmc: davinci_mmc: Use sg_miter for PIO")
Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
Link: https://lore.kernel.org/r/20240711081838.47256-2-bastien.curutchet@bootlin.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>