riscv: Fix wrong usage of __pa() on a fixmap address

riscv: Fix wrong usage of __pa() on a fixmap address

riscv uses fixmap addresses to map the dtb so we can't use __pa() which
is reserved for linear mapping addresses.

Fixes: b2473a359763 ("of/fdt: add dt_phys arg to early_init_dt_scan and early_init_dt_verify")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20241209074508.53037-1-alexghiti@rivosinc.com
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>