If the read fails we kmap an error code.  This doesn't end well.  Instead
print a critical error and pray.  This mirrors the rest of the fs
behaviour with critical error cases.

Acked-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Acked-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>