target/ppc: Fix size of struct PPCElfPrstatus

gdb refuses to parse QEMU memory dumps because struct PPCElfPrstatus
is the wrong size. Fix it.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Fixes: e62fbc54 ("target-ppc: dump-guest-memory support")
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

target/ppc/arch_dump.c

@@ -50,7 +50,7 @@ struct PPCUserRegStruct {
 struct PPCElfPrstatus {
     char pad1[112];
     struct PPCUserRegStruct pr_reg;
-    reg_t pad2[4];
+    char pad2[40];
 } QEMU_PACKED;