X86, Acer, WMI: Do not double include linux/dmi.h in acer-wmi.c

Including linux/dmi.h once in drivers/platform/x86/acer-wmi.c is enough.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Reviewed-by: Lee, Chun-Yi <jlee@novell.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>