vc_screen: modify vcs_size() handling in vcs_read()

[ Upstream commit 46d733d0efc79bc8430d63b57ab88011806d5180 ]

Restore the vcs_size() handling in vcs_read() to what
it had been in previous version.

Fixes: 226fae124b2d ("vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF")
Suggested-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: George Kennedy <george.kennedy@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>