scsi: scsi_transport_srp: Fix a couple of kernel-doc warnings

Add a struct short description and a function return value to prevent
kernel-doc warnings:

scsi_transport_srp.h:77: warning: missing initial short description on line:
 * struct srp_function_template
scsi_transport_srp.h:132: warning: No description found for return value of 'srp_chkready'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20240408025425.18778-9-rdunlap@infradead.org
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>