ext4: remove redundant assignment to error

Variable error is set to zero but this value is never read as it's not
used later on, hence it is a redundant assignment and can be removed.

Cleans up the following clang-analyzer warning:

fs/ext4/ioctl.c:657:3: warning: Value stored to 'error' is never read
[clang-analyzer-deadcode.DeadStores].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1619691409-83160-1-git-send-email-jiapeng.chong@linux.alibaba.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>