drivers/thermal/spear_thermal.c: use devm_clk_get

devm_clk_get allocates a resource that is released when a driver detaches.
This patch uses devm_clk_get for data that is allocated in the probe
function of a platform device and is only released in the remove function.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>