iomap: Fix conflicting values of iomap flags

IOMAP_F_ATOMIC_BIO mistakenly took the same value as of IOMAP_F_SIZE_CHANGED
in patch '370a6de7651b ("iomap: rework IOMAP atomic flags")'.
Let's fix this and let's also create some more space for filesystem reported
flags to avoid this in future. This patch makes the core iomap flags to start
from bit 15, moving downwards. Note that "flags" member within struct iomap
is of type u16.

Fixes: 370a6de ("iomap: rework IOMAP atomic flags")
Signed-off-by: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20250327170119.61045-1-ritesh.list@gmail.com
Reviewed-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: riteshharjani

include/linux/iomap.h

@@ -78,6 +78,11 @@ struct vm_fault;
 #define IOMAP_F_ANON_WRITE	(1U << 7)
 #define IOMAP_F_ATOMIC_BIO	(1U << 8)
 
+/*
+ * Flag reserved for file system specific usage
+ */
+#define IOMAP_F_PRIVATE		(1U << 12)
+
 /*
  * Flags set by the core iomap code during operations:
  *
@@ -88,14 +93,8 @@ struct vm_fault;
  * range it covers needs to be remapped by the high level before the operation
  * can proceed.
  */
-#define IOMAP_F_SIZE_CHANGED	(1U << 8)
-#define IOMAP_F_STALE		(1U << 9)
-
-/*
- * Flags from 0x1000 up are for file system specific usage:
- */
-#define IOMAP_F_PRIVATE		(1U << 12)
-
+#define IOMAP_F_SIZE_CHANGED	(1U << 14)
+#define IOMAP_F_STALE		(1U << 15)
 
 /*
  * Magic value for addr: