[media] af9015: Don't use dynamic static allocation

Dynamic static allocation is evil, as Kernel stack is too low, and
compilation complains about it on some archs:
	drivers/media/usb/dvb-usb-v2/af9015.c:433:1: warning: 'af9015_eeprom_hash' uses dynamic stack allocation [enabled by default]
In this specific case, it is a gcc bug, as the size is a const, but
it is easy to just change it from const to a #define, getting rid of
the gcc warning.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>