lib/sysfs: rename devname functions, cleanup

lib/sysfs: rename devname functions, cleanup

Well, I don't have mental power to use function names like

 sysfs_devname_to_dev_name()

so this patch renames to

 sysfs_devname_sys_to_dev()
 sysfs_devname_dev_to_sys()

It also cleanups usage of the functions. We have to be sure that
sysfs.c code returns regular devnames. The existence of the sysfs
devnames (with '!') should be completely hidden in sysfs specific
code.

Signed-off-by: Karel Zak <kzak@redhat.com>