depmod: do not output .bin to stdout

depmod: do not output .bin to stdout

index_write() relies on fseek/ftell to manage the position to which we
are write and thus needs the file stream to support it.

Right now when trying to write the index to stdout we fail with:

	depmod: tools/depmod.c:416: index_write: Assertion `initial_offset >= 0' failed.
	Aborted (core dumped)

We have no interest in outputting our index to stdout, so just skip it
like is done with other indexes.

While at it, add/remove some newlines to improve readability.

Reported-by: Yanko Kaneti <yaneti@declera.com>
Fix: b866b2165ae6 ("Lookup aliases in the modules.builtin.modinfo")