filelock: fl_pid field should be signed int

This field has been unsigned for a very long time, but most users of the
struct file_lock and the file locking internals themselves treat it as a
signed value. Change it to be pid_t (which is a signed int).
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20240131-flsplit-v3-1-c6129007ee8d@kernel.orgReviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

include/linux/filelock.h

@@ -98,7 +98,7 @@ struct file_lock {
 	fl_owner_t fl_owner;
 	unsigned int fl_flags;
 	unsigned char fl_type;
-	unsigned int fl_pid;
+	pid_t fl_pid;
 	int fl_link_cpu;		/* what cpu's list is this on? */
 	wait_queue_head_t fl_wait;
 	struct file *fl_file;