_blocks being non-zero instead.

Fix jffs2_reserve_space() to wait for the in-progress erases to
complete, when jffs2_garbage_collect_pass() returns -EAGAIN.

And fix jffs2_erase_succeeded() to actually wake up the erase_wait wq
that jffs2_reserve_space() is now using.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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