firmware/dmi_scan: drop obsolete comment

This comment predates the introduction of early_ioremap.  Since then the
missing calls to dmi_iounmap have been added by Ingo and Yinghai in
commits 0d64484f ("x86: fix DMI ioremap leak") and 3212bff3
("x86: left over fix for leak of early_ioremp in dmi_scan") .  That was
over 5 years ago so it is about time to drop this now misleading
comment.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>