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

In the Linux kernel, the following vulnerability has been resolved: 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.