hw/riscv/boot: Check the error of fdt_pack()

Coverity reports that we don't check the error result of fdt_pack(), so
let's save the result and assert that it is 0.

Fixes: Coverity CID 1458136
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 07325315b49d5555269f76094e4bc5296e0643b9.1626303527.git.alistair.francis@wdc.com

hw/riscv/boot.c

@@ -182,7 +182,7 @@ uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
 {
     uint32_t temp, fdt_addr;
     hwaddr dram_end = dram_base + mem_size;
-    int fdtsize = fdt_totalsize(fdt);
+    int ret, fdtsize = fdt_totalsize(fdt);
 
     if (fdtsize <= 0) {
         error_report("invalid device-tree");
@@ -198,7 +198,9 @@ uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
     temp = MIN(dram_end, 3072 * MiB);
     fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 16 * MiB);
 
-    fdt_pack(fdt);
+    ret = fdt_pack(fdt);
+    /* Should only fail if we've built a corrupted tree */
+    g_assert(ret == 0);
     /* copy in the device tree */
     qemu_fdt_dumpdtb(fdt, fdtsize);