of: Add of_property_read_u16_index

There is an of_property_read_u32_index and of_property_read_u64_index.
This patch adds a similar helper for u16.

Signed-off-by: Ernest Van Hoecke <ernest.vanhoecke@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20250319142059.46692-2-francesco@dolcini.it


Signed-off-by: Mark Brown <broonie@kernel.org>