rpmsg: glink: spi: Fix idr and channel refcounts

Each kref_put represents a cleanup for an open function. Remove the
extra kref put and rely on transport remove to cleanup any defunct
channels. Remove the idr from the lcid and rcid lists since the idr is
added on the open calls. This prevents any references to the dangling
pointers after cleanup.

Change-Id: I5c78ab17b716f5dea36b5d23ed2888ad5743edbf
Signed-off-by: Chris Lew <clew@codeaurora.org>