powerpc/ftrace: Use size macro instead of opencoding

0x80000000 is SZ_2G. Use it.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix comparison against unsigned -SZ_2G]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/bb6626e884acffe87b58736291df57db3deaa9b9.1652074503.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/trace/ftrace.c

@@ -741,7 +741,7 @@ int __init ftrace_dyn_arch_init(void)
 #endif
 	long reladdr = addr - kernel_toc_addr();
 
-	if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
+	if (reladdr >= SZ_2G || reladdr < -(long)SZ_2G) {
 		pr_err("Address of %ps out of range of kernel_toc.\n",
 				(void *)addr);
 		return -1;