NOR/core bugfix: restore invariants

NOR/core bugfix: restore invariants

The The patch labeled "CFI CORE: bug-fix protect single sector" was merged
rged without some requested bugfixes.  Most significantly it broke invariants
in the code, invalidating descriptions and changing the calling convention
for underlying drivers.  (It (Also wasn't CFI-specific...)

Fix that, and Include an update from Antonio Borneo for the degenerate
"nothing to do" case, (although that's still in the  wrong location.  which
is presumably why that is it was working in some cases but not all.)

 src/flash/nor/core.c |   21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>