linux-wandboard

ext4: allow a NULL argument to ext4_ext_drop_refs()

Teach ext4_ext_drop_refs() to accept a NULL argument, much like
kfree().  This allows us to drop a lot of checks to make sure path is
non-NULL before calling ext4_ext_drop_refs().

Signed-off-by: Theodore Ts'o <tytso@mit.edu>