scsi: core: Safe warning about bad dev info string

Both "model" and "strflags" are passed to "%s" even when one or both are
NULL.

It is safe because vsprintf() would detect the NULL pointer and print
"(null)". But it is a kernel-specific feature and compiler warns about it:

<warning>
   In file included from include/linux/kernel.h:19,
                    from arch/x86/include/asm/percpu.h:27,
                    from arch/x86/include/asm/current.h:6,
                    from include/linux/sched.h:12,
                    from include/linux/blkdev.h:5,
                    from drivers/scsi/scsi_devinfo.c:3:
   drivers/scsi/scsi_devinfo.c: In function 'scsi_dev_info_list_add_str':
>> include/linux/printk.h:434:44: warning: '%s' directive argument is null [-Wformat-overflow=]
     434 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
         |                                            ^
   include/linux/printk.h:430:3: note: in definition of macro 'printk_index_wrap'
     430 |   _p_func(_fmt, ##__VA_ARGS__);    \
         |   ^~~~~~~
   drivers/scsi/scsi_devinfo.c:551:4: note: in expansion of macro 'printk'
     551 |    printk(KERN_ERR "%s: bad dev info string '%s' '%s'"
         |    ^~~~~~
   drivers/scsi/scsi_devinfo.c:552:14: note: format string is defined here
     552 |           " '%s'\n", __func__, vendor, model,
         |              ^~
</warning>

Do not rely on the kernel specific behavior and print the message a safe
way.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401112002.AOjwMNM0-lkp@intel.com/Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240111162419.12406-1-pmladek@suse.comReviewed-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_devinfo.c

@@ -551,9 +551,9 @@ static int scsi_dev_info_list_add_str(char *dev_list)
 		if (model)
 			strflags = strsep(&next, next_check);
 		if (!model || !strflags) {
-			printk(KERN_ERR "%s: bad dev info string '%s' '%s'"
-			       " '%s'\n", __func__, vendor, model,
-			       strflags);
+			pr_err("%s: bad dev info string '%s' '%s' '%s'\n",
+			       __func__, vendor, model ? model : "",
+			       strflags ? strflags : "");
 			res = -EINVAL;
 		} else
 			res = scsi_dev_info_list_add(0 /* compatible */, vendor,