SS_FSUpdate: Fix to cast into bigger type before operation

SS_FSUpdate: Fix to cast into bigger type before operation

Since the operands are int, SS_UINT32(unsigned int) and long type, it is
required to cast them into a big enough type before adding them.
(Thier value are all non-negative values)

To resolve this issue, operands are casted to uint64_t, which is big
enough to store the value of the variables and the result of the
arithmetic operation.

Change-Id: Iecf8ffa3be11984ce6fdc3d850f9b9c9f74c7186
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>