relay: use kasprintf() instead of fixed buffer formatting

Improve readability and maintainability by replacing a hard coded string
allocation and formatting by using the kasprintf() helper.

It also eliminates the GCC compiler warning (with CONFIG_WERROR=y, which
is default, it becomes an error:

kernel/relay.c:357:42: error: `snprintf' output may be truncated before the last format character [-Werror=format-truncation=]

Link: https://lkml.kernel.org/r/20250317212948.1811176-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: andy-shev

kernel/relay.c

@@ -351,10 +351,9 @@ static struct dentry *relay_create_buf_file(struct rchan *chan,
 	struct dentry *dentry;
 	char *tmpname;
 
-	tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
+	tmpname = kasprintf(GFP_KERNEL, "%s%d", chan->base_filename, cpu);
 	if (!tmpname)
 		return NULL;
-	snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
 
 	/* Create file in fs */
 	dentry = chan->cb->create_buf_file(tmpname, chan->parent,