tcl/target/nrf52: fix nrf52_recover

tcl/target/nrf52: fix nrf52_recover

nrf52_recover was merged in pre "Handle Tcl return values consistently"
state - remove ocd_ prefixes.

Erase and unlock sequence was changed to comply Nordic semiconductor
recommendation:
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fnwp_027%2FWP%2Fnwp_027%2FnWP_027_erasing.html

Change-Id: Ic54236c27cf25ad8091e9e572ba1ef846f0d47c2
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reported-by: Pieter De Gendt <pieter.degendt@gmail.com>
Reviewed-on: http://openocd.zylin.com/5845
Tested-by: jenkins
Reviewed-by: Pieter De Gendt <pieter.degendt@gmail.com>