scripts: ubinize-image.sh: fix support for static volume

scripts: ubinize-image.sh: fix support for static volume

Apart from being misspelled ('dymamic' vs. 'dynamic') and a mismatch of
the number of parameters, there is also simply no need to add the 'dynamic'
volume type keyword as 6th parameter as that's the default anyway.
Fix and simplify the ubinize-image.sh script to work as intended.

Fixes: 6c17d71973 ("scripts: ubinize-image.sh: support static volumes, make size optional")
Reported-by: Hannu Nyman <hannu.nyman@iki.fi>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>