md/raid5: separate large if clause out of fetch_block().

fetch_block() has a very large and hard to read 'if' condition.

Separate it into its own function so that it can be
made more readable.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2015-02-02 11:32:23 +11:00
commit 2c58f06e6f