user_namespace: remove unnecessary NULL values from kbuf

kbuf is assigned first, so it does not need to initialize the assignment.

Link: https://lkml.kernel.org/r/20240115062519.31298-1-zeming@nfschina.com
Signed-off-by: Li zeming <zeming@nfschina.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/user_namespace.c

@@ -931,7 +931,7 @@ static ssize_t map_write(struct file *file, const char __user *buf,
 	struct uid_gid_map new_map;
 	unsigned idx;
 	struct uid_gid_extent extent;
-	char *kbuf = NULL, *pos, *next_line;
+	char *kbuf, *pos, *next_line;
 	ssize_t ret;
 
 	/* Only allow < page size writes at the beginning of the file */