V4L/DVB (7317): pvrusb2: Increase buffer size for printing video standard strings

Buffer size for printing pvrusb2 video standard strings was too small
before.  This is cosmetic; the printing logic is not able to overrun a
too-short buffer.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>