include/linux/dmar.h: forward-declare struct acpi_dmar_header

x86_64 allnoconfig:

In file included from arch/x86/kernel/pci-dma.c:3:
include/linux/dmar.h:248: warning: 'struct acpi_dmar_header' declared inside parameter list
include/linux/dmar.h:248: warning: its scope is only this definition or declaration, which is probably not what you want

Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/dmar.h

@@ -26,6 +26,8 @@
 #include <linux/msi.h>
 #include <linux/irqreturn.h>
 
+struct acpi_dmar_header;
+
 /* DMAR Flags */
 #define DMAR_INTR_REMAP		0x1
 #define DMAR_X2APIC_OPT_OUT	0x2