scsi: target: Simplify target_lu_gp_members_show()

scsi: target: Simplify target_lu_gp_members_show()

Remove the stack buffer 'buf'. This patch does not modify the output
produced by target_lu_gp_members_show().

An example of the output that is produced with this patch applied:

$ cat /sys/kernel/config/target/core/alua/lu_gps/default_lu_gp/members
fileio_0/vdev0
fileio_1/vdev1
iblock_0/vdev2
$ od -c /sys/kernel/config/target/core/alua/lu_gps/default_lu_gp/members
0000000   f   i   l   e   i   o   _   0   /   v   d   e   v   0  \n   f
0000020   i   l   e   i   o   _   1   /   v   d   e   v   1  \n   i   b
0000040   l   o   c   k   _   0   /   v   d   e   v   2  \n
0000055

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20251027184639.3501254-3-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>