jesd219: fix alignment

Previously we added the bssplit option to accommodate more advanced
blocksize lists.  However, blockalign appears to default to the smallest
element in the bssplit list.  If so, we must update the example JESD219
workload to explicitly specify blockalign=4k, to satisfy the JESD219
workload requirement ("data payloads greater than or equal to 4096 bytes
are aligned on 4k boundaries").  There is no explicit alignment
requirement for <4KB blocksizes, so at this time, there seems to be no
need to specify a separate alignment for some blocksizes in bssplit
list.

Signed-off-by: Jens Axboe <axboe@fb.com>