doc: starfive: use consistent formatting

Always use ---- for the H2 level.

Reviewed-by: E Shattow <e@freeshell.de>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/board/starfive/milk-v_mars.rst b/doc/board/starfive/milk-v_mars.rst
index 554932e..aba9c9c 100644
--- a/doc/board/starfive/milk-v_mars.rst
+++ b/doc/board/starfive/milk-v_mars.rst
@@ -8,7 +8,7 @@
 accordingly.
 
 Building
-~~~~~~~~
+--------
 
 1. Add the RISC-V toolchain to your PATH.
 2. Setup ARCH & cross compilation environment variable:
@@ -40,7 +40,7 @@
 as the FIT image (u-boot.itb) with OpenSBI and U-Boot.
 
 Device-tree selection
-~~~~~~~~~~~~~~~~~~~~~
+---------------------
 
 Depending on the board version U-Boot set variable $fdtfile to either
 starfive/jh7110-starfive-visionfive-2-v1.2a.dtb or
@@ -58,14 +58,14 @@
 provide a default value.
 
 Boot source selection
-~~~~~~~~~~~~~~~~~~~~~
+---------------------
 
 The board provides the DIP switches MSEL[1:0] to select the boot device out of
 SPI flash, eMMC, SD-card, UART. To select booting from SD-card set the DIP
 switches MSEL[1:0] to 10.
 
 Preparing the SD-Card
-~~~~~~~~~~~~~~~~~~~~~
+---------------------
 
 The device firmware loads U-Boot SPL (u-boot-spl.bin.normal.out) from the
 partition with type GUID 2E54B353-1271-4842-806F-E436D6AF6985. You are free
@@ -106,6 +106,6 @@
 	sudo umount /mnt
 
 Booting
-~~~~~~~
+-------
 
 Once you plugin the sdcard and power up, you should see the U-Boot prompt.