fs: add i_blocksize()

Replace all 1 << inode->i_blkbits and (1 << inode->i_blkbits) in fs
branch.

This patch also fixes multiple checkpatch warnings: WARNING: Prefer
'unsigned int' to bare use of 'unsigned'

Thanks to Andrew Morton for suggesting more appropriate function instead
of macro.

[geliangtang@gmail.com: truncate: use i_blocksize()]
  Link: http://lkml.kernel.org/r/9c8b2cd83c8f5653805d43debde9fa8817e02fc4.1484895804.git.geliangtang@gmail.com
Link: http://lkml.kernel.org/r/1481319905-10126-1-git-send-email-fabf@skynet.be
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 18e5146..c1d2a07 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2875,7 +2875,7 @@
 		if (!ret)
 			ret = btrfs_prealloc_file_range(inode, mode,
 					range->start,
-					range->len, 1 << inode->i_blkbits,
+					range->len, i_blocksize(inode),
 					offset + len, &alloc_hint);
 		else
 			btrfs_free_reserved_data_space(inode, range->start,