UBI: introduce a new IO return code

This patch introduces the %UBI_IO_BAD_HDR_READ return code for
the I/O level function. We will use this code in order to distinguish
between "corrupted header possibly because this is non-ubi data" and
"corrupted header possibly because of real data corruption and ECC error".

So far this patch does not introduce any functional change, just a
preparation.

This patch is pased on a patch from
Sebastian Andrzej Siewior <sebastian@breakpoint.cc>

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Tested-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 539b3f6..0359e0c 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -90,12 +90,15 @@
  * UBI_IO_PEB_FREE: the physical eraseblock is free, i.e. it contains only a
  *                  valid erase counter header, and the rest are %0xFF bytes
  * UBI_IO_BAD_HDR: the EC or VID header is corrupted (bad magic or CRC)
+ * UBI_IO_BAD_HDR_READ: the same as %UBI_IO_BAD_HDR, but also there was a read
+ * 			error reported by the flash driver
  * UBI_IO_BITFLIPS: bit-flips were detected and corrected
  */
 enum {
 	UBI_IO_PEB_EMPTY = 1,
 	UBI_IO_PEB_FREE,
 	UBI_IO_BAD_HDR,
+	UBI_IO_BAD_HDR_READ,
 	UBI_IO_BITFLIPS
 };