rust: macros: enable use of hyphens in module names

Some modules might need naming that contains hyphens "-" to match the
auto-probing by name in the platform devices that comes from the device
tree.

But Rust identifier cannot contain hyphens, so replace them with
underscores.

Signed-off-by: Anisse Astier <anisse@astier.eu>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
[ Viresh: Replace "-" with '-', minor commit log fix, rename variable and
  fix line length checkpatch warnings ]
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>