Fix PMC Pm25LV512 and Pm25LV010 probing.

Apparently PMC did not understand the purpose of the JEDEC
continuation code. These chips reply to RES (the only supported ID
command) with the prefix-less vendor ID, a device ID, eventually
followed by the continuation byte for the vendor ID.

This fix uses only the first two bytes instead of appending the
continuation code to the device ID. The problem was reported by The
Raven who also tested the fix on a Pm25LV010 (with an imprint of
"Pm25LV010E").

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>

git-svn-id: svn://flashrom.org/flashrom/trunk@1806 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1