thermal: re-name thermal.c to thermal_sys.c

thermal_sys was already the name of the resulting module,
and it is built from  this one source file.
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/thermal/Makefile

@@ -2,5 +2,4 @@
 # Makefile for sensor chip drivers.
 #
 
-thermal_sys-objs	+= thermal.o
 obj-$(CONFIG_THERMAL)		+= thermal_sys.o