ata: libata-eh: Rename no_dipm variable to be more clear

Rename the no_dipm variable to host_has_dipm, by inverting the
expression, and and also having a clearer name.

No functional change.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>