hikey960: Fixup the hisi-bootloader flashall script

I realized in some cases the cache partition in the hisi-bootloader
doesn't play well with the fastboot format command, so add explicit
format/size to get it to work more reliably.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Change-Id: Iccb0f3a497011fd523bea4947202c434855c9b9a
diff --git a/installer/hikey960/flash-all.sh b/installer/hikey960/flash-all.sh
index a2c97a0..3f8bf9b 100755
--- a/installer/hikey960/flash-all.sh
+++ b/installer/hikey960/flash-all.sh
@@ -26,5 +26,5 @@
 fastboot flash dts "${ANDROID_PRODUCT_OUT}"/dt.img
 fastboot flash super "${ANDROID_PRODUCT_OUT}"/super.img
 fastboot flash userdata "${ANDROID_PRODUCT_OUT}"/userdata.img
-fastboot format cache
+fastboot format:ext4:10000000 cache
 fastboot reboot