lightnvm/pblk-gc: Delete an error message for a failed memory allocation in...

lightnvm/pblk-gc: Delete an error message for a failed memory allocation in pblk_gc_line_prepare_ws()

Omit an extra message for a memory allocation failure in this function.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>