powerpc/ftrace: Inline ftrace_modify_code()

Inlining ftrace_modify_code(), it increases a bit the
size of ftrace code but brings 5% improvment on ftrace
activation.

Usually in C files we let gcc decide what to do but here
it really help to 'help' gcc to decide to inline, thought
we don't want to force it with an __always_inline that
would be too much for CONFIG_CC_OPTIMIZE_FOR_SIZE.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1597a06d57cfc80e6853838c4066e799bf6c7977.1652074503.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/trace/ftrace.c

@@ -53,7 +53,7 @@ ftrace_call_replace(unsigned long ip, unsigned long addr, int link)
 	return op;
 }
 
-static int
+static inline int
 ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
 {
 	ppc_inst_t replaced;