scsi: sg: Don't use GFP_ATOMIC in sg_start_req()

scsi: sg: Don't use GFP_ATOMIC in sg_start_req()

sg_start_req() is called from normal user context and can sleep when
waiting for memory.  Switch it to use GFP_KERNEL, which fixes allocation
failures seen with the bio_alloc rework.

Fixes: b520c4eef83d ("block: split bio_alloc_bioset more clearly into a fast and slowpath")
Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20260415060813.807659-2-hch@lst.de
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>