doc: usage: reorder commands in index.rst

Reorder alphabetically the command in the index of usage
in U-Boot documentation.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index c1f9b6a..41b247b 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -34,12 +34,12 @@
    load
    loady
    mbr
-   mmc
    md
+   mmc
    pstore
    qfw
+   reset
    sbi
+   scp03
    size
    true
-   scp03
-   reset