UBI: improve ECC error message

ECC errors are quite typical errors on NAND, so it is worth improving
the UBI message and print something like

ubi_io_read: error -74 (ECC error) while reading 4096 bytes from PEB 1:4 ...

rather than

ubi_io_read: error -74 while reading 4096 bytes from PEB 1:4 ...

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>