fix superiotool for NCT6776F

fix superiotool for NCT6776F

The current code exits config mode of the NCT6776F immediately after
detection, so the register dump shows all 0xffs. This patch adds code to
re-enter config mode for the register dump so that the register contents
can be read.

Change-Id: I4ad0c108b6411a665e31f55dea4b91ca77d1a5f7
Signed-off-by: Florian Zumbiehl <florz@florz.de>
Reviewed-on: http://review.coreboot.org/391
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>