Now that the pvrusb2 driver can dynamically choose which inputs to
make available depending on the hardware, the enumeration of input
choices is no longer a contiguous range of integers.  Unfortunately
this causes a problem in the v4l2 implementation since the input
enumeration requires continuity in the API.  This change implements a
mapping in order to preserve the v4l2 interface requirement.
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>