dyndbg-docs: initialization is done early, not arch

since cf964976484 in 2012, initialization is done with early_initcall,
update the Docs, which still say arch_initcall.

Acked-by: <jbaron@akamai.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20200719231058.1586423-3-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/admin-guide/dynamic-debug-howto.rst

@@ -250,8 +250,8 @@ the syntax described above, but must not exceed 1023 characters.  Your
 bootloader may impose lower limits.
 
 These ``dyndbg`` params are processed just after the ddebug tables are
-processed, as part of the arch_initcall.  Thus you can enable debug
-messages in all code run after this arch_initcall via this boot
+processed, as part of the early_initcall.  Thus you can enable debug
+messages in all code run after this early_initcall via this boot
 parameter.
 
 On an x86 system for example ACPI enablement is a subsys_initcall and::