drm/msm/gem: prevent integer overflow in msm_ioctl_gem_submit()

In the Linux kernel, the following vulnerability has been resolved: drm/msm/gem: prevent integer overflow in msm_ioctl_gem_submit() The "submit->cmd[i].size" and "submit->cmd[i].offset" variables are u32 values that come from the user via the submit_lookup_cmds() function. This addition could lead to an integer wrapping bug so use size_add() to prevent that. Patchwork: https://patchwork.freedesktop.org/patch/624696/