jffs2: print symbolic error name instead of error code

Utilize the %pe print specifier to get the symbolic error name as a
string (i.e "-ENOMEM") in the log message instead of the error code to
increase its readablility.

This change was suggested in
https://lore.kernel.org/all/92972476-0b1f-4d0a-9951-af3fc8bc6e65@suswa.mountain/Signed-off-by: Christian Heusel <christian@heusel.eu>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/jffs2/background.c

@@ -44,8 +44,8 @@ int jffs2_start_garbage_collect_thread(struct jffs2_sb_info *c)
 
 	tsk = kthread_run(jffs2_garbage_collect_thread, c, "jffs2_gcd_mtd%d", c->mtd->index);
 	if (IS_ERR(tsk)) {
-		pr_warn("fork failed for JFFS2 garbage collect thread: %ld\n",
-			-PTR_ERR(tsk));
+		pr_warn("fork failed for JFFS2 garbage collect thread: %pe\n",
+			tsk);
 		complete(&c->gc_thread_exit);
 		ret = PTR_ERR(tsk);
 	} else {