libnvme-wrap: exit on VOID_FN lookup failure

libnvme-wrap: exit on VOID_FN lookup failure

libnvme-wrap provides fallbacks for missing libnvme functions.
For functions that return a value, the FN() macro can be used
to define a default return value if the function isn't found.
This isn't possible for functions returning void,
so VOID_FN() currently is a no-op if the function can't be found.
For nvme_init_copy_range_f1(), the only current VOID_FN() user,
this will result in silently sending a Copy command
with a zeroed range, which is not what the user requested.
Instead, exit the process immediately if the function can't be found.

Signed-off-by: Caleb Sander <csander@purestorage.com>