cifs_permission() doesn't need to bail out in RCU mode

nothing potentially blocking except generic_permission(), which
will DTRT
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/cifs/cifsfs.c

@@ -257,9 +257,6 @@ static int cifs_permission(struct inode *inode, int mask, unsigned int flags)
 {
 	struct cifs_sb_info *cifs_sb;
 
-	if (flags & IPERM_FLAG_RCU)
-		return -ECHILD;
-
 	cifs_sb = CIFS_SB(inode->i_sb);
 
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_PERM) {