dm: core: Fix dm_extended_scan_fdt()

This function  takes an argument, blob,
but never uses it, instead uses gd->fdt_blob directly.

Fixes: e81c9864 ("dm: core: add clocks node scan")

Reported-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>