[PATCH] driver core: fix unnecessary NULL check in drivers/base/class.c

This patch tries to fix an issue in drivers/base/class.c, please
review and apply if correct.

Patch Description:
  "parent_class" is checked for NULL already, so removed the unnecessary
  check.

Signed-off-by: Jayachandran C. <c.jayachandran@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>