backlight: qcom-wled: Use cpu_to_le16 macro to perform conversion

The kernel already provides appropriate primitives to perform endianness
conversion which should be used in favour of manual bit-wrangling.

Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211115203459.1634079-4-marijn.suijten@somainline.org