Add missing return on module init error

Add 'return' before 'SBK_MODULE_INIT_ERROR' when module initialization
fails due to a missing dependency. This appears to have been
accidentally lost in 0b1f8df512047c6ace60701180ec1e4f6e97484e.

Change-Id: I1bc1453c8515e7b67c101c8e8f13a1266d04433f
Reviewed-by: John Ehresman <jpe@wingware.com>