tcl: update to new syntax of telnet command

Commit ad21613618 ("server/telnet: Restructure commands")
modifies the syntax.

	sed -i 's/telnet_port/telnet port/'

Change-Id: If1ad34a1ec54824dbc124acd36a894862276a34f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8502
Reviewed-by: zapb <dev@zapb.de>
Tested-by: jenkins

tcl/target/u8500.cfg

@@ -143,7 +143,7 @@ proc enable_apetap {} {
 	}
 
 tcl port 5555
-telnet_port 4444
+telnet port 4444
 gdb port 3333
 
 if { [info exists CHIPNAME] } {