examples/nvme/hello_world: call exit() on read error

The printout in read_complete() says "Read I/O failed, aborting run",
however, execution still continues, and prints and prints the buffer
where the result was supposed to be stored.
Since we got a read error, we will not have gotten any data stored
in the buffer, so it is simply confusing to print it.

Calling exit() in the read_complete() error handling code code also
makes it consistent with the error handling code in write_complete()
and reset_zone_complete().

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Change-Id: I6e542758c57efc376f921857c2cdb24e252d49c6
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4837


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>