hw/alpha: Fix compiler warning (integer constant is too large)

hw/alpha: Fix compiler warning (integer constant is too large)

From buildbot default_i386_rhel61:

  CC    alpha-softmmu/hw/alpha/typhoon.o
hw/alpha/typhoon.c: In function 'typhoon_translate_iommu':
hw/alpha/typhoon.c:703: warning: integer constant is too large for 'long' type
hw/alpha/typhoon.c:703: warning: integer constant is too large for 'long' type

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>