Remove kmem_cache_alloc return value cast.
Coccinelle emits the following warning:
./fs/9p/vfs_inode.c:226:12-29: WARNING: casting value returned by memory allocation function to (struct v9fs_inode *) is useless.
Link: http://lkml.kernel.org/r/1596013140-49744-1-git-send-email-liheng40@huawei.com
Signed-off-by: Li Heng <liheng40@huawei.com>
[Dominique: commit message wording]
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>