module: Assign the index before calling init()

module: Assign the index before calling init()

Any code that runs inside the init() callback sees an invalid module
index. Sometimes init() does things that cause hooks to be fired. This
means that any code that uses hooks may see an invalid module index.
Fix this by assigning the module index before init() is called.

There are no known issues in the upstream code base where an invalid
module index would be used, but an out-of-tree module
(module-murphy-ivi) had a problem with this.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=63923