keys: fix missing __user in KEYCTL_PKEY_QUERY

The arg5 of KEYCTL_PKEY_QUERY should have a __user pointer tag on
it as it is a user pointer. This clears the following sparse warning
for this:

security/keys/keyctl.c:1755:43: warning: incorrect type in argument 3 (different address spaces)
security/keys/keyctl.c:1755:43:    expected struct keyctl_pkey_query [noderef] <asn:1>*<noident>
security/keys/keyctl.c:1755:43:    got struct keyctl_pkey_query *<noident>

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: James Morris <james.morris@microsoft.com>