sr: simplify the local variable initialization in sr_block_open()

sr: simplify the local variable initialization in sr_block_open()

Commit 01d0c698536f ("sr: implement ->free_disk to simplify refcounting")
refactored sr_block_open(), initialized one variable with a duplicate
assignment (probably an unintended copy & paste duplication) and turned one
error case into an early return, which makes the initialization of the
return variable needless.

So, simplify the local variable initialization in sr_block_open() to make
the code a bit more clear.

No functional change. No change in resulting object code.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220314150321.17720-1-lukas.bulwahn@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>