greybus: Revert "protocol.c: fix a kernel panic caused by __gb_protocol_register"

This reverts commit 57131bf309d34568dd3b8f8e9da7a7ba25e9495e, it isn't
going to be needed as the patch this fixes will be reverted.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>