f2fs: remove redundant assignment to variable err

The assignment to variable err is redundant since the code jumps to
label next and err is then re-assigned a new value on the call to
sanity_check_node_chain. Remove the assignment.

Cleans up clang scan build warning:
fs/f2fs/recovery.c:464:6: warning: Value stored to 'err' is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>