debugfs: restore and tweak original error messaging

debugfs: restore and tweak original error messaging

In response to reviewer comments, commit fe56188b07 included changes
that modified some of the code used to output error messages when
checking user-supplied block numbers.  These changes converted calls
to parse_ulonglong() to calls to strtoblk().  Because strtoblk() calls
parse_ulonglong(), and both output error messages, two redundant and
relatively generic messages were output on each error.

Fix this by removing the error message output from strtoblk(), and
extending it to accept an optional error message argument that it
supplies in lieu of a default to parse_ulonglong().  Also, revert to
the more descriptive original error messages with mods per reviewer
comments, and fix an error message in do_replace_node().

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>