thermal: remove const flag from .ops of imx thermal

As per previous changes on thermal framework API,
registering a new thermal zone does not require
a const thermal zone ops.

Thus, this patch removes the flag from imx thermal zone ops.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>