MIPS: head.S: Init fw_passed_dtb to builtin DTB

Init the 'fw_passed_dtb' pointer to the buit-in Device Tree blob when it
has been compiled in with CONFIG_BUILTIN_DTB.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/kernel/head.S

@@ -111,6 +111,12 @@ NESTED(kernel_entry, 16, sp)			# kernel entry point
 	move		t2, a1
 	beq		a0, t1, dtb_found
 
+#ifdef CONFIG_BUILTIN_DTB
+	PTR_LA	t2, __dtb_start
+	PTR_LA	t1, __dtb_end
+	bne		t1, t2, dtb_found
+#endif /* CONFIG_BUILTIN_DTB */
+
 	li		t2, 0
 dtb_found:
 #endif /* CONFIG_USE_OF */