Ensure that the DMA delay does not get rounded down to zero ticks when
a timeout value of a single tick is given. With FreeBSD-10 and newer
the current system time is used as a starting point, and the minimum
callout time of a single tick will be guaranteed. This patch mostly
affect the DMA delay timeouts, which are typically in the range from
0.125 to 2ms.

MFC after: 1 week