drm/amdkfd: fix sysfs topology prop length on buffer truncation

drm/amdkfd: fix sysfs topology prop length on buffer truncation

sysfs_show_gen_prop() accumulated snprintf()'s return value into the
offset. snprintf() reports bytes that would have been written, not
bytes actually written, so a truncated sysfs show could over-report
its length. Use sysfs_emit_at(), which returns only the bytes written.

Signed-off-by: Yongqiang Sun <Yongqiang.Sun@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>