Use a constant instead of sizeof(int) for SSE2 immediate constant.

Apparently gcc-4.8.2 was not able to evaluate sizeof(int) to the
constant 4 at compile time, but thought it was either a 64-bit
value or a non-const value. Since the register sizes are fixed
we simply hardcode the value 4 bytes instead.

Change-Id: If739b733727b032eb7e5b7fa0a75e7cd51989a0b