staging: slicoss: return status of slic_link_event_handler

slic_link_event_handler() issues command READ_LINK_STATUS to be executed
asynchronously, which is followed by UP configuration write command. But
it can fail while setting up the command and in that case the link will
not be up. Lets check the status and return it.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>