sysfs: fix warning when creating a sysfs group without attributes

When attempting to create a gropu without attrs, the warning prints the
name of the group.  However, the check for name being a NULL pointer is
wrong: it uses the pointer to the name when it's NULL.  Fix it to use
the name if present, otherwise just put an empty string.

Cc: Bruno Prémont <bonbons@linux-vserver.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>