binman: test: Rename 172_fit_fdt.dts to 170_fit_fdt.dts

Currently there are 2 binman test cases using the same 172 number.
It seems that 172_fit_fdt.dts was originally named as 170_, but
commit c0f1ebe9 ("binman: Allow selecting default FIT configuration")
changed its name to 172_ for no reason. Let's change it back.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>