Fix silly icc remark #2259

Another stupid remark to quiet out:

remark #2259: non-pointer conversion from "int" to "UINT16={unsigned short}"
may lose significant bits

In this case icc always converts to an integer the result of a shift operation
if the bit size of the operand is smaller, hence the warning when assignin
back to n.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>