doc: board: ti: am64x: Fix build step numbering

Fix up build step numbering.

Fixes: 4bf49bade124 ("doc: board: ti: am64: Add boot flow diagram")
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
1 file changed