common: cli_hush: avoid dead code

common: cli_hush: avoid dead code

Condition "(value == NULL && ++value == NULL)" actully will
always return false.

Instead, use condition "(value == NULL || *(value + 1) == 0)" to detect
such expression "c=". To "c=", *(value + 1) is 0, so directly return -1,
but not continue.

Signed-off-by: Peng Fan <[email protected]>
Cc: Rabin Vincent <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Tom Rini <[email protected]>
Reviewed-by: Simon Glass <[email protected]>