pstore/blk: Use "%lu" to format unsigned long

On 32-bit:

    fs/pstore/blk.c: In function ‘__best_effort_init’:
    include/linux/kern_levels.h:5:18: warning: format ‘%zu’ expects argument of type ‘size_t’, but argument 3 has type ‘long unsigned int’ [-Wformat=]
	5 | #define KERN_SOH "\001"  /* ASCII Start Of Header */
	  |                  ^~~~~~
    include/linux/kern_levels.h:14:19: note: in expansion of macro ‘KERN_SOH’
       14 | #define KERN_INFO KERN_SOH "6" /* informational */
	  |                   ^~~~~~~~
    include/linux/printk.h:373:9: note: in expansion of macro ‘KERN_INFO’
      373 |  printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
	  |         ^~~~~~~~~
    fs/pstore/blk.c:314:3: note: in expansion of macro ‘pr_info’
      314 |   pr_info("attached %s (%zu) (no dedicated panic_write!)\n",
	  |   ^~~~~~~

Cc: [email protected]
Fixes: 7bb9557 ("pstore/blk: Use the normal block device I/O path")
Signed-off-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: Jens Axboe <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/pstore/blk.c

@@ -309,7 +309,7 @@ static int __init __best_effort_init(void)
 	if (ret)
 		kfree(best_effort_dev);
 	else
-		pr_info("attached %s (%zu) (no dedicated panic_write!)\n",
+		pr_info("attached %s (%lu) (no dedicated panic_write!)\n",
 			blkdev, best_effort_dev->zone.total_size);
 
 	return ret;