[media] tw5864: remove double irq lock code

As warned by smatch:
	drivers/media/pci/tw5864/tw5864-core.c:160 tw5864_h264_isr() error: double lock 'irqsave:flags'
	drivers/media/pci/tw5864/tw5864-core.c:174 tw5864_h264_isr() error: double unlock 'irqsave:flags'

Remove the IRQ duplicated lock.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>