scsi: qedf: use correct strncpy() size

gcc-8 warns during link-time optimization that the strncpy() call passes
the size of the source buffer rather than the destination:

drivers/scsi/qedf/qedf_dbg.c: In function 'qedf_uevent_emit':
include/linux/string.h:253: error: 'strncpy' specified bound depends on the length of the source argument [-Werror=stringop-overflow=]

This changes it to strscpy() with the correct length, guaranteeing a
properly nul-terminated string of the right size.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Chad Dupuis <chad.dupuis@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>