RISC-V: Make some header guards more specific

Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Signed-off-by: Michael Clark <mjc@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

include/hw/riscv/virt.h

@@ -16,8 +16,8 @@
  * this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef HW_VIRT_H
-#define HW_VIRT_H
+#ifndef HW_RISCV_VIRT_H
+#define HW_RISCV_VIRT_H
 
 typedef struct {
     /*< private >*/