ovl: fix wrong flags check in FS_IOC_FS[SG]ETXATTR ioctls

[ Upstream commit 941d935ac7636911a3fd8fa80e758e52b0b11e20 ]

The ioctl argument was parsed as the wrong type.

Fixes: b21d9c435f93 ("ovl: support the FS_IOC_FS[SG]ETXATTR ioctls")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>