Remove exit call from sys_physmap_*.

All callers are prepared to handle error if ERROR_PTR is returned.
The Manpage mentioning the respective return code is readapted.

Signed-off-by: Niklas Söderlund <niso@kth.se>
Acked-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>

git-svn-id: svn://flashrom.org/flashrom/trunk@1744 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1