boards: disco_l475_iot1 update openocd.cfg

Latest versions of OpenOCD don't seem to work with
`transport select hla_swd`, but the `board/stm32l4discovery.cfg`
file should work on any version of OpenOCD that contains it
(including my older version).

This should keep things forward-compatible.

Probably this will affect other stm32 boards using `hla_swd`
but I have no way of testing them.

Signed-off-by: Glenn Andrews <[email protected]>

Author: glenn-andrews

boards/st/disco_l475_iot1/support/openocd.cfg

@@ -1,7 +1 @@
-source [find interface/stlink.cfg]
-
-transport select hla_swd
-
-source [find target/stm32l4x.cfg]
-
-reset_config srst_only
+source [find board/stm32l4discovery.cfg]