mfd: Add MODULE_DEVICE_TABLE to vx855

The device table is required to load modules based on modaliases.
After adding the MODULE_DEVICE_TABLE, below entries will be added to
modules.pcimap:
vx855                0x00001106 0x00008409 0xffffffff 0xffffffff 0x00000000 0x00000000 0x0

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Harald Welte <laforge@gnumonks.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>