ext4: convert number of blocks to clusters properly

commit 810da240f221d64bf90020f25941b05b378186fe upstream.

We're using macro EXT4_B2C() to convert number of blocks to number of
clusters for bigalloc file systems.  However, we should be using
EXT4_NUM_B2C().

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Lingzhu Xiang <lxiang@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>