[media] saa7115: Don't use a dynamic array

At least on s390, gcc complains about that:
    drivers/media/i2c/saa7115.c: In function 'saa711x_detect_chip.constprop.2':
    drivers/media/i2c/saa7115.c:1647:1: warning: 'saa711x_detect_chip.constprop.2' uses dynamic stack allocation [enabled by default]

While for me the above report seems utterly bogus, as the
compiler should be optimizing saa711x_detect_chip, merging
it with saa711x_detect_chip and changing:
	char chip_ver[size - 1];
to
	char chip_ver[16];

because this function is only called on this code snippet:
	char name[17];
	...
	ident = saa711x_detect_chip(client, id, name, sizeof(name));

It seems that gcc is not optimizing it, at least on s390.

As getting rid of it is easy, let's do it.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>