doc: Correct position of gdb '--args' parameter

The '--args' parameter to gdb comes before the binary that the debugger
will be attached to rather than after the binary and before the
arguments. Fix that in the docs.

Signed-off-by: Andrew Scull <ascull@google.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/tests_sandbox.rst b/doc/develop/tests_sandbox.rst
index 84608dc..40cf8ec 100644
--- a/doc/develop/tests_sandbox.rst
+++ b/doc/develop/tests_sandbox.rst
@@ -103,7 +103,7 @@
 
 You can easily use gdb on these tests, without needing --gdbserver::
 
-   $ gdb u-boot --args -T -c "ut dm gpio"
+   $ gdb --args u-boot -T -c "ut dm gpio"
    ...
    (gdb) break dm_test_gpio
    Breakpoint 1 at 0x1415bd: file test/dm/gpio.c, line 37.