hw/ufs: Fix incorrect comment for segment_size and allocation_unit_size

hw/ufs: Fix incorrect comment for segment_size and allocation_unit_size

The comments for segment_size and allocation_unit_size incorrectly
described them as 4KB. According to the UFS specification,
segment_size is expressed in units of 512 bytes.
Given segment_size = 0x2000 (8192), the actual size is 4MB.
Similarly, allocation_unit_size = 1 means 1 segment = 4MB.

This patch updates the comments to reflect the correct size.

Signed-off-by: Keoseong Park <keosung.park@samsung.com>
Reviewed-by: Jeuk Kim <jeuk20.kim@samsung.com>
Message-ID: <20250403092140epcms2p355a7f039871b3e5b409754ef450b9158@epcms2p3>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>