ACPI: thermal_lib: include "internal.h" for function prototypes

The newly added functions are declared in a header that is not included
before the definition:

drivers/acpi/thermal_lib.c:46:5: error: no previous prototype for 'acpi_active_trip_temp' [-Werror=missing-prototypes]
   46 | int acpi_active_trip_temp(struct acpi_device *adev, int id, int *ret_temp)
      |     ^~~~~~~~~~~~~~~~~~~~~
drivers/acpi/thermal_lib.c:57:5: error: no previous prototype for 'acpi_passive_trip_temp' [-Werror=missing-prototypes]
   57 | int acpi_passive_trip_temp(struct acpi_device *adev, int *ret_temp)
      |     ^~~~~~~~~~~~~~~~~~~~~~
drivers/acpi/thermal_lib.c:63:5: error: no previous prototype for 'acpi_hot_trip_temp' [-Werror=missing-prototypes]
   63 | int acpi_hot_trip_temp(struct acpi_device *adev, int *ret_temp)
      |     ^~~~~~~~~~~~~~~~~~
drivers/acpi/thermal_lib.c:69:5: error: no previous prototype for 'acpi_critical_trip_temp' [-Werror=missing-prototypes]
   69 | int acpi_critical_trip_temp(struct acpi_device *adev, int *ret_temp)
      |     ^~~~~~~~~~~~~~~~~~~~~~~

Fixes: 6908097a

 ("ACPI: thermal_lib: Add functions returning temperature in deci-Kelvin")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>