spidernet: fix error interrupt handling

In addition to the value of GHIINT0STS, spidernet interrupt handler
should check the values of GHIINT1STS/GHIINT2STS registers at the
beginning of spider_net_interrupt() so as not to drop error
interrupts.

GHIINT1STS/GHIINT2STS registers indicates some of erroneous conditions
in spidernet, and a few bits of GHIINT0STS register reflects these
conditions. But GHIINT0MSK masks these bits, so you should check these
conditions by reading GHIINT1STS/GHIINT2STS registers directly.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Jens Osterkamp <jens@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>