btrfs: avoid uninitialized variable warning

With CONFIG_SMP and CONFIG_PREEMPT both disabled, gcc decides
to partially inline the get_state_failrec() function but cannot
figure out that means the failrec pointer is always valid
if the function returns success, which causes a harmless
warning:

fs/btrfs/extent_io.c: In function 'clean_io_failure':
fs/btrfs/extent_io.c:2131:4: error: 'failrec' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This marks get_state_failrec() and set_state_failrec() both
as 'noinline', which avoids the warning in all cases for me,
and seems less ugly than adding a fake initialization.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 47dc196a ("btrfs: use proper type for failrec in extent_state")
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -1842,7 +1842,7 @@ u64 count_range_bits(struct extent_io_tree *tree,
  * set the private field for a given byte offset in the tree.  If there isn't
  * an extent_state there already, this does nothing.
  */
-static int set_state_failrec(struct extent_io_tree *tree, u64 start,
+static noinline int set_state_failrec(struct extent_io_tree *tree, u64 start,
 		struct io_failure_record *failrec)
 {
 	struct rb_node *node;
@@ -1870,7 +1870,7 @@ static int set_state_failrec(struct extent_io_tree *tree, u64 start,
 	return ret;
 }
 
-static int get_state_failrec(struct extent_io_tree *tree, u64 start,
+static noinline int get_state_failrec(struct extent_io_tree *tree, u64 start,
 		struct io_failure_record **failrec)
 {
 	struct rb_node *node;