drm/amdkfd: Fix memory leak in kfd_mem_dmamap_userptr()

In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: Fix memory leak in kfd_mem_dmamap_userptr() If the number of pages from the userptr BO differs from the SG BO then the allocated memory for the SG table doesn't get freed before returning -EINVAL, which may lead to a memory leak in some error paths. Fix this by checking the number of pages before allocating memory for the SG table.