btrfs: Remove isize local variable in compress_file_range

It's used only once so just inline the call to i_size_read. The
semantics regarding the inode size are not changed, the pages in the
range are locked and i_size cannot change between the time it was set
and used.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -453,7 +453,6 @@ static noinline void compress_file_range(struct inode *inode,
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	u64 blocksize = fs_info->sectorsize;
 	u64 actual_end;
-	u64 isize = i_size_read(inode);
 	int ret = 0;
 	struct page **pages = NULL;
 	unsigned long nr_pages;
@@ -467,7 +466,7 @@ static noinline void compress_file_range(struct inode *inode,
 	inode_should_defrag(BTRFS_I(inode), start, end, end - start + 1,
 			SZ_16K);
 
-	actual_end = min_t(u64, isize, end + 1);
+	actual_end = min_t(u64, i_size_read(inode), end + 1);
 again:
 	will_compress = 0;
 	nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;