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 <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Josh Poimboeuf <[e-mail]>
Cc: [e-mail]
Cc: Masami Hiramatsu <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: "Steven Rostedt (VMware)" <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: x86-ml <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/kernel/ftrace_32.S

···
 # 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)