btrfs: remove unnecessary pg_offset assignments in __extent_writepage()

We're initializing pg_offset to 0, setting it immediately, then
reassigning it to 0 again after. The former became unnecessary in
211c17f5 ("Fix corners in writepage and btrfs_truncate_page"). The
latter is a leftover that should've been removed in 40f76580
("Btrfs: split up __extent_writepage to lower stack usage"). Remove
both.
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3562,7 +3562,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 	u64 page_end = start + PAGE_SIZE - 1;
 	int ret;
 	int nr = 0;
-	size_t pg_offset = 0;
+	size_t pg_offset;
 	loff_t i_size = i_size_read(inode);
 	unsigned long end_index = i_size >> PAGE_SHIFT;
 	unsigned long nr_written = 0;
@@ -3591,8 +3591,6 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 		flush_dcache_page(page);
 	}
 
-	pg_offset = 0;
-
 	set_page_extent_mapped(page);
 
 	if (!epd->extent_locked) {