powerpc/xmon: Fix build when 4xx=y and 44x=n

dump_tlb_44x() is only defined when 44x=y, but the ifdef in xmon.c
checks for 4xx, leading to a build failure:

  arch/powerpc/xmon/xmon.c:912:4: error: implicit declaration of function 'dump_tlb_44x'
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/xmon/xmon.c

@@ -907,7 +907,7 @@ cmds(struct pt_regs *excp)
 		case 'u':
 			dump_segments();
 			break;
-#elif defined(CONFIG_4xx)
+#elif defined(CONFIG_44x)
 		case 'u':
 			dump_tlb_44x();
 			break;