affs: initialize fsdata in affs_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.

Fixes: f2b6a16e ("fs: affs convert to new aops")
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/affs/file.c

@@ -880,7 +880,7 @@ affs_truncate(struct inode *inode)
 	if (inode->i_size > AFFS_I(inode)->mmu_private) {
 		struct address_space *mapping = inode->i_mapping;
 		struct page *page;
-		void *fsdata;
+		void *fsdata = NULL;
 		loff_t isize = inode->i_size;
 		int res;