i2c-dev: Return correct error code on class_create() failure

In Linus' tree:
http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commit;h=e74783ec3cb981211689bd2cfd3248f8dc48ec01



We need to convert the error pointer from class_create(), else we'll return the
successful return code from register_chrdev() on failure.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>