nfs: direct: drop useless initializer in nfs_direct_write_completion()

nfs: direct: drop useless initializer in nfs_direct_write_completion()

In nfs_direct_write_completion(), the local variable req isn't used outside
the *while* loop and is assigned to right at the start of that loop's body,
so its initializer appears useless -- drop it; then move the declaration to
the loop body (which happens to have a pointless empty line anyway)...

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Link: https://lore.kernel.org/r/416219f5-7983-484b-b5a7-5fb7da9561f7@omp.ru
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>