ARM: uniphier: allow debug_ll_init() to do nothing for unknown SoCs

This function should just return for unknown SoCs rather than writing
unexpected values to registers.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/mach-uniphier/arm32/debug_ll.S

@@ -175,6 +175,7 @@ proxstream2_end:
 	b		init_uart
 ph1_ld6b_end:
 #endif
+	mov		pc, lr
 
 init_uart:
 	addruart	r0, r1, r2