pata_hpt3x2n: clarify about HPT371N support

Commit 28e21c8c (pata_hpt3x2n: Add HPT371N
support and other bits) forgot to update the driver's Kconfig entry, heading
comment, and module description (that also wrongly claims support of HPT302)
which may confuse users...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>