ARMv8: fix error in freeing stack frame

relocate_code() allocates 32 bytes stack frame but only 16 bytes are
freed before return. it will cause errors to possible previous frames
and doesn't make relocate_code() look like a function.

fix by freeing 32 bytes stack space

Signed-off-by: zijun_hu <zijun_hu@htc.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/lib/relocate_64.S

@@ -73,6 +73,6 @@ relocate_done:
 	isb	sy
 4:	ldp	x0, x1, [sp, #16]
 	bl	__asm_flush_dcache_range
-5:	ldp	x29, x30, [sp],#16
+5:	ldp	x29, x30, [sp],#32
 	ret
 ENDPROC(relocate_code)