powerpc/ftrace: Use STK_GOT in ftrace_mprofile.S

Instead of open coding offset value 24, use STK_GOT when
accessing got register in stack.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9042bb30fa972056715fe5b6598a7c8049681293.1645099283.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/trace/ftrace_mprofile.S

@@ -82,7 +82,7 @@
 
 #ifdef CONFIG_PPC64
 	/* Save callee's TOC in the ABI compliant location */
-	std	r2, 24(r1)
+	std	r2, STK_GOT(r1)
 	ld	r2,PACATOC(r13)	/* get kernel TOC in r2 */
 
 	addis	r3,r2,function_trace_op@toc@ha
@@ -140,7 +140,7 @@
 
 #ifdef CONFIG_PPC64
 	/* Restore callee's TOC */
-	ld	r2, 24(r1)
+	ld	r2, STK_GOT(r1)
 #endif
 
 	/* Pop our stack frame */