mm/mprotect: remove the redundant initialization for error

The variable error will be assigned correctly before it is used, the
initialization is redundant, so remove it.

Link: https://lkml.kernel.org/r/20220704114112.163112-1-xiujianfeng@huawei.com


Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>