hw/misc/imx_ccm.c: Add missing VMState list terminator

The VMStateDescription for the imx_ccm device was missing its
terminator. Found by static search of the codebase using
a regex based on one suggested by Ian Jackson:
  pcregrep -rMi '(?s)VMStateField(?:(?!END_OF_LIST).)*?;' $(git grep -l 'VMStateField\[\]')

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-stable@nongnu.org