When moving a PEB the leb_write_trylock() function is called.
As the function never returns 0 UBI will end up in an endless
loop.

Noticed the issue when fastmap has been enabled and data is beeing copied
several times to a UBI volume. When UBI tries to move the anchor PEB,
the issue comes up.

The leb_write_trylock() is now equal to the leb_write_lock().
But kept it for easier maintaince in future when syncing with
kernel.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>