drm/i915/gt: Fixed "CPU" -> "GPU" typo

Column header should be GPU, not CPU

Signed-off-by: Zhang He <zhanghe9702@163.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240913140721.31165-1-zhanghe9702@163.com