tty: vt: simplify ansi_control_string()

tty: vt: simplify ansi_control_string()

Given all the ANSI control states are sequential in the vc_ctl_state
enum, we can define first/last constants and use them in
ansi_control_string(). It makes the test simple and allows for removal
of the 'if' (which was unnecessary at all -- the 'return' should have
returned the 'if' content directly anyway).

And remove the useless comment -- it's clear from the function
prototype.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20240202065608.14019-17-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>