media: go7007: add check of return value of go7007_read_addr()

If go7007_read_addr() returns error channel is not assigned a value.
In this case go to allocfail.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 866b8695

 ("Staging: add the go7007 video driver")
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>