[MTD] block2mtd: logging typo fixes

Address a number of small issues mainly regarding the output made by this
driver to dmesg:

- Some of the blkmtd's had not been changed to block2mtd which caused
  display problem

- the parse_err() macro was displaying "block2mtd: " twice

Signed-off-by: Stéphane Chazelas <stephane.chazelas@emerson.com>
Acked-by: Jörn Engel <joern@lazybastard.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>