crypto: ccree - remove bogus paragraph about freeing SRAM

The SRAM allocator does not support deallocating memory.
Hence remove all references to freeing SRAM.

Fix grammar while at it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>