[media] tm6000: fix OOPS at tm6000_ir_int_stop() and tm6000_ir_int_start()

[ 3755.608233] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
[ 3755.616360] IP: [<ffffffffa03b80b7>] tm6000_ir_int_stop+0x10/0x1b [tm6000]

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