platform: generic: Constify FDT pointers in fw_platform_init()

Indicate that none of these functions modify the devicetree by
constifying the parameter type.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

platform/generic/include/platform_override.h

@@ -29,7 +29,7 @@ struct platform_override {
 	int (*extensions_init)(const struct fdt_match *match,
 			       struct sbi_hart_features *hfeatures);
 	int (*pmu_init)(const struct fdt_match *match);
-	void (*fw_init)(void *fdt, const struct fdt_match *match);
+	void (*fw_init)(const void *fdt, const struct fdt_match *match);
 	int (*vendor_ext_provider)(long funcid,
 				   struct sbi_trap_regs *regs,
 				   struct sbi_ecall_return *out,