of: unittest: fix warning on PowerPC frame size warning

The struct device variable "dev_bogus" was triggering this warning
on a PowerPC build:

    drivers/of/unittest.c: In function 'of_unittest_dma_ranges_one.constprop':
    [...] >> The frame size of 1424 bytes is larger than 1024 bytes
             [-Wframe-larger-than=]

This variable is now dynamically allocated.

Fixes: e0d07278

 ("dma-mapping: introduce DMA range map, supplanting dma_pfn_offset")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211210184636.7273-2-jim2101024@gmail.com