[mv] Fix invalid condition in fdt_fixup_ranges

Add parentheses to perform assignment before comparison. The prior
condition worked because fdt_parent_addr_cells returns 1 for the DTB
on which fdt_fixup_ranges is called and accidentally par_addr_cells
ends up to be set to the same value.

PR: 210705
Submitted by: David Binderman <dcb314@hotmail.com>
MFC after: 1 week