Since commit 67e67df8 ("gta02: Use pcf50633 backlight driver instead
of platform backlight driver.") the list of gta02 pmu children is empty
therefore looping through it and adding devices is a no-op.

This also fixes the GCC v8.1 W=1 warning:

    arch/arm/mach-s3c24xx/mach-gta02.c: In function 'gta02_pmu_attach_child_devices':
    arch/arm/mach-s3c24xx/mach-gta02.c:538:16: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
      for (n = 0; n < ARRAY_SIZE(gta02_devices_pmu_children); n++)
                    ^
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>