[media] mantis: cleanup a warning

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
drivers/media/pci/mantis/mantis_i2c.c: In function 'mantis_i2c_init':
drivers/media/pci/mantis/mantis_i2c.c:222:15: warning: variable 'intmask' set but not used [-Wunused-but-set-variable]
  u32 intstat, intmask;