crypto: caam - fix warning in APPEND_MATH_IMM_u64

An implicit truncation is done when using a variable of 64 bits
in MATH command:

warning: large integer implicitly truncated to unsigned type [-Woverflow]

Silence the compiler by feeding it with an explicit truncated value.

Signed-off-by: Tudor Ambarus <tudor.ambarus@freescale.com>
Signed-off-by: Horia Geant? <horia.geanta@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>