nvdimm: Remove empty if statement

This patch removes an empty statement from an if expression and promotes
the else statement to the if expression with the expression logic reversed.

I feel this is more readable as the empty statement can lead to issues if
any additional logic was ever added.

Reviewed-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>