crypto: ccree - use existing helpers to split 64-bit addresses

Use the existing lower_32_bits() and upper_32_bits() macros instead of
explicit casts and shifts to split a 64-bit address in its two 32-bit
parts.
Drop the superfluous cast to "u16", as the FIELD_PREP() macro already
masks it to the specified field width.

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