igc: Set buffer type for empty frames in igc_init_empty_frame

igc: Set buffer type for empty frames in igc_init_empty_frame

Set the buffer type to IGC_TX_BUFFER_TYPE_SKB for empty frame in the
igc_init_empty_frame function. This ensures that the buffer type is
correctly identified and handled during Tx ring cleanup.

Fixes: db0b124f02ba ("igc: Enhance Qbv scheduling by using first flag bit")
Cc: stable@vger.kernel.org # 6.2+
Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>