staging: most: define iface_to_hdm as an inline function

Convert `iface_to_hdm` macro into a static inline function.
it is not great to have macro that use `container_of` macro,
because from looking at the definition one cannot tell
what type it applies to.

One can get the same benefit from an efficiency point of view
by making an inline function.

Suggested-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Menna Mahmoud <eng.mennamahmoud.mm@gmail.com>
Link: https://lore.kernel.org/r/20230320212239.22452-1-eng.mennamahmoud.mm@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>