btrfs-progs: docs: fix typo in device stats name read_io_errs

The value is called read_io_errs elsewhere.

Pull-request: #1032
Signed-off-by: Robert Joslyn <robert.joslyn@redrectangle.org>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: bobolopolis

Documentation/btrfs-device.rst

@@ -230,7 +230,7 @@ filesystem lifetime or from a scrub run.
 write_io_errs
         Failed writes to the block devices, means that the layers beneath the
         filesystem were not able to satisfy the write request.
-read_io_errors
+read_io_errs
         Read request analogy to write_io_errs.
 flush_io_errs
         Number of failed writes with the *FLUSH* flag set. The flushing is a method of