media: usbvision-i2c: fix format overflow warning

media: usbvision-i2c: fix format overflow warning

gcc-7 notices that we copy a fixed length string into another
string of the same size, with additional characters:

drivers/media/usb/usbvision/usbvision-i2c.c: In function 'usbvision_i2c_register':
drivers/media/usb/usbvision/usbvision-i2c.c:190:36: error: '%d' directive writing between 1 and 11 bytes into a region of size between 0 and 47 [-Werror=format-overflow=]
  sprintf(usbvision->i2c_adap.name, "%s-%d-%s", i2c_adap_template.name,
                                    ^~~~~~~~~~
drivers/media/usb/usbvision/usbvision-i2c.c:190:2: note: 'sprintf' output between 4 and 76 bytes into a destination of size 48

Using snprintf() makes the code more robust in general, but will still
trigger a possible warning about truncation in the string.
We know this won't happen as the template name is always "usbvision", so
we can easily avoid the warning as well by using this as the format string
directly.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>