sata_sil24: sil24_interrupt() micro-optimisation

sil24_interrupt() loads host->ports[i] into a local variable,
validates it, and then loads the value again in the call to
sil24_host_intr(). This patch replaces the second load by a
reference to the local variable.

This is safe since no side-effects have occurred since the
initial load. It also improves readability since it makes
it clear that the parameter to sil24_host_intr() is the same
value which was just validated.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Jeff Garzik <jeff@garzik.org>