hfs: make splice write available again

hfs: make splice write available again

Since 5.10, splice() or sendfile() return EINVAL. This was
caused by commit 36e2c7421f02 ("fs: don't allow splice read/write
without explicit ops").

This patch initializes the splice_write field in file_operations, like
most file systems do, to restore the functionality.

Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20250529140033.2296791-2-frank.li@vivo.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>