scsi: lpfc: Use struct_group() to initialize struct lpfc_cgn_info

scsi: lpfc: Use struct_group() to initialize struct lpfc_cgn_info

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark "stat" region of struct lpfc_cgn_info that
should be initialized to zero, and refactor the "data" region memset()
to wipe everything up to the cgn_stats region.

Link: https://lore.kernel.org/r/20211208195957.1603092-1-keescook@chromium.org
Reviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>