The ftrace callback prototype was changed to pass a special ftrace_regs
instead of pt_regs as the last parameter, but the static ftrace for nds32
missed updating ftrace_trace_function and this caused a warning when
compared to ftrace_stub:

../arch/nds32/kernel/ftrace.c: In function '_mcount':
../arch/nds32/kernel/ftrace.c:24:35: error: comparison of distinct pointer types lacks a cast [-Werror]
   24 |         if (ftrace_trace_function != ftrace_stub)
      |                                   ^~

Link: https://lore.kernel.org/all/20211027055554.19372-1-rdunlap@infradead.org/
Link: https://lkml.kernel.org/r/20211027125101.33449969@gandalf.local.home

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: d19ad077 ("ftrace: Have the callbacks receive a struct ftrace_regs instead of pt_regs")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>