vc_screen: rewrite vcs_size to accept vc, not inode

[ Upstream commit 71d4abfa ]

It is weird to fetch the information from the inode over and over. Read
and write already have the needed information, so rewrite vcs_size to
accept a vc, attr and unicode and adapt vcs_lseek to that.

Also make sure all sites check the return value of vcs_size for errors.

And document it using kernel-doc.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200818085706.12163-5-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 8fb9ea65 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF")
Signed-off-by: Sasha Levin <sashal@kernel.org>