x86/paravirt: Fix some warning messages

x86/paravirt: Fix some warning messages

The first argument to WARN_ONCE() is a condition.

Fixes: 5800dc5c19f3 ("x86/paravirt: Fix spectre-v2 mitigations for paravirt guests")
Signed-off-by: Dan Carpenter <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Alok Kataria <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/20180919103553.GD9238@mwanda