Documentation: firmware-guide: ACPI: fix table alignment in namespace.rst

Fixe the alignment in the ACPI block diagram (RST table)
by adding missing spaces
Signed-off-by: Vilhelm Prytz <vilhelm@prytznet.se>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/firmware-guide/acpi/namespace.rst

@@ -56,13 +56,13 @@ are illustrated in the following diagram::
                   +- - - -+                  |  +-------------------| |
                   | Entry | - - - - - - - -+ |  | Definition Blocks | |
                   +- - - -+                | |  +-------------------+ |
-                                          | |  +- - - - - - - - - -+ |
-                                          +-|->|       SSDT        | |
+                                           | |  +- - - - - - - - - -+ |
+                                           +-|->|       SSDT        | |
                                              |  +-------------------+ |
                                              |  | Definition Blocks | |
                                              |  +- - - - - - - - - -+ |
                                              +------------------------+
-                                                         |
+                                                          |
                                              OSPM Loading |
                                                          \|/
                                                    +----------------+