[media] tw5864-core: remove excessive irqsave

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'

Two different spinlocks are obtained, so having two calls is correct,
but second irqsave is superfluous, and using same "flags" variable is
just wrong.

Reported-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Andrey Utkin <andrey.utkin@corp.bluecherry.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>