powerpc/security: make display of branch cache flush more consistent

Make the count-cache and link-stack messages look the same

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200609070610.846703-4-npiggin@gmail.com