fs: tighten a sanity check in file_attr_to_fileattr()

fs: tighten a sanity check in file_attr_to_fileattr()

The fattr->fa_xflags is a u64 that comes from the user.  This is a sanity
check to ensure that the users are only setting allowed flags.  The
problem is that it doesn't check the upper 32 bits.  It doesn't really
affect anything but for more flexibility in the future, we want to enforce
users zero out those bits.

Fixes: be7efb2d20d6 ("fs: introduce file_getattr and file_setattr syscalls")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/baf7b808-bcf2-4ac1-9313-882c91cc87b2@sabinyo.mountain
Signed-off-by: Christian Brauner <brauner@kernel.org>