rockchip: misc: fix misc_read() return check

misc_read() is documented to return the number of bytes read or a
negative error value.  The Rockchip drivers currently do not implement
this correctly and instead return zero on success or a negative error
value.

In preparation for fixing the drivers, fix the condition here to only
error on negative values.

Suggested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/misc.c b/arch/arm/mach-rockchip/misc.c
index 849014d..7d03f0c 100644
--- a/arch/arm/mach-rockchip/misc.c
+++ b/arch/arm/mach-rockchip/misc.c
@@ -83,7 +83,7 @@
 
 	/* read the cpu_id range from the efuses */
 	ret = misc_read(dev, cpuid_offset, cpuid, cpuid_length);
-	if (ret) {
+	if (ret < 0) {
 		debug("%s: reading cpuid from the efuses failed\n",
 		      __func__);
 		return -1;