nfs: Remove bogus assignment

Commit 3a6fd1f0 (pnfs/blocklayout: remove read-modify-write handling
in bl_write_pagelist) introduced a bogus assignment pg_index = pg_index
in variable initialization. AFAICS it's just a typo so remove it.
Spotted by Coverity (id 1248711).

CC: Christoph Hellwig <hch@lst.de>
Signed-off-by: NJan Kara <jack@suse.cz>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/blocklayout/blocklayout.c

@@ -378,7 +378,7 @@ bl_write_pagelist(struct nfs_pgio_header *header, int sync)
 	loff_t offset = header->args.offset;
 	size_t count = header->args.count;
 	struct page **pages = header->args.pages;
-	int pg_index = pg_index = header->args.pgbase >> PAGE_CACHE_SHIFT;
+	int pg_index = header->args.pgbase >> PAGE_CACHE_SHIFT;
 	unsigned int pg_len;
 	struct blk_plug plug;
 	int i;