riscv/efi_stub: Fix get_boot_hartid_from_fdt() return value
The get_boot_hartid_from_fdt() function currently returns U32_MAX
for failure case which is not correct because U32_MAX is a valid
hartid value. This patch fixes the issue by returning error code.
Cc: <stable@vger.kernel.org> Fixes: d7071743db31 ("RISC-V: Add EFI stub support.") Signed-off-by: Sunil V L <sunilvl@ventanamicro.com> Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>