KVM: ARM/arm64: avoid returning negative error code as bool

KVM: ARM/arm64: avoid returning negative error code as bool

is_valid_cache returns true if the specified cache is valid.
Unfortunately, if the parameter passed it out of range, we return
-ENOENT, which ends up as true leading to potential hilarity.

This patch returns false on the failure path instead.

Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
(cherry picked from commit 18d457661fb9fa69352822ab98d39331c3d0e571)
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>