device-dax: Avoid an unnecessary check in alloc_dev_dax_range()

Swap the calling sequence of krealloc() and __request_region(), call the
latter first. In this way, the value of dev_dax->nr_range does not need to
be considered when __request_region() failed.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20201219081840.1149-2-thunder.leizhen@huawei.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>