lift generic_write_checks() into callers of __generic_file_write_iter()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/block_dev.c
Simple merge

diff --cc fs/cifs/file.c
Simple merge

diff --cc fs/ext4/file.c
Simple merge

diff --cc fs/udf/file.c
Simple merge

diff --cc mm/filemap.c
Simple merge