rust: replace <linux/module.h> with <linux/export.h> in rust/exports.c

<linux/export.h> is the right header to include for using
EXPORT_SYMBOL_GPL. <linux/module.h> includes much more bloat.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20231124142617.713096-1-masahiroy@kernel.org


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>