thermal: qoriq: Simplify the 'site' variable assignment

There is no need to assign zero to the variable 'site' and then
perform a compound bitwise OR operation afterwards.

Make it simpler by assigning the final 'site' value directly.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>