dmi: fix kernel-doc notation

Add missing kernel-doc notation:

drivers/firmware/dmi_scan.c:475: No description found for parameter 'str'
drivers/firmware/dmi_scan.c:592: No description found for parameter 'f'
drivers/firmware/dmi_scan.c:592: No description found for parameter 'str'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>