fs: hfsplus: initialize fsdata in hfsplus_file_truncate()

fs: hfsplus: initialize fsdata in hfsplus_file_truncate()

When aops->write_begin() does not initialize fsdata, KMSAN may report an
error passing the latter to aops->write_end().

Fix this by unconditionally initializing fsdata.

Link: https://lkml.kernel.org/r/20221121112134.407362-5-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Chao Yu <chao@kernel.org>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>