x86/asm/ftrace: Mark function_hook as function

Relabel function_hook to be marked really as a function. It is called
from C and has the same expectations towards the stack etc.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-arch@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191011115108.12392-22-jslaby@suse.cz

arch/x86/kernel/ftrace_32.S

@@ -21,9 +21,9 @@ EXPORT_SYMBOL(__fentry__)
 # define MCOUNT_FRAME			0	/* using frame = false */
 #endif
 
-ENTRY(function_hook)
+SYM_FUNC_START(function_hook)
 	ret
-END(function_hook)
+SYM_FUNC_END(function_hook)
 
 ENTRY(ftrace_caller)