crypto: inside-secure - unify cache reset

This patch unify the way the cache related data is zeroed when the cache
buffer is DMA unmapped. It should not change the driver behaviour, but
improves the code safety and readability.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>