x86/msi: Fix msi message data shadow struct

The x86 MSI message data is 32 bits in total and is either in
compatibility or remappable format, see Intel Virtualization Technology
for Directed I/O, section 5.1.2.

Fixes: 6285aa50 ("x86/msi: Provide msi message shadow structs")
Co-developed-by: Adrian-Ken Rueegsegger <ken@codelabs.ch>
Signed-off-by: Adrian-Ken Rueegsegger <ken@codelabs.ch>
Signed-off-by: Reto Buerki <reet@codelabs.ch>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220407110647.67372-1-reet@codelabs.ch

arch/x86/include/asm/msi.h

@@ -12,14 +12,17 @@ int pci_msi_prepare(struct irq_domain *domain, struct device *dev, int nvec,
 /* Structs and defines for the X86 specific MSI message format */
 
 typedef struct x86_msi_data {
+	union {
+		struct {
 			u32	vector			:  8,
 				delivery_mode		:  3,
 				dest_mode_logical	:  1,
 				reserved		:  2,
 				active_low		:  1,
 				is_level		:  1;
-
+		};
 		u32	dmar_subhandle;
+	};
 } __attribute__ ((packed)) arch_msi_msg_data_t;
 #define arch_msi_msg_data	x86_msi_data