UPSTREAM: module: unexport find_module and module_mutex

find_module is not used by modular code any more, and random driver code
has no business calling it to start with.

Bug: 157965270
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
(cherry picked from commit 089049f6)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: If736b690e00331156626ff41de224628f5aed7c5