dmi: prevent linked list corruption

Adding the same item to a given linked list more than once is guaranteed
to break and corrupt the list.  This is however what we do in dmi_scan
since commit 79da4721

 ("x86: fix DMI out
of memory problems").

Given that there is absolutely no interest in saving empty OEM strings
anyway, I propose the simple and efficient fix below: we discard the empty
OEM strings altogether.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Parag Warudkar <parag.warudkar@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Matt Domsch <Matt_Domsch@dell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>