Avoid overflow that may occur from math operations.
Coverity message:
-----------------
CID 457888: (#1 of 1): Overflowed constant (INTEGER_OVERFLOW)34.
overflow_const: Expression acc, where base is known to be equal to 16,
overflows the type of acc, which is type unsigned long long.
Change-Id: I41f22e22625a17826b2cedff101120918e23c8e8
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>