Add suffix LL to constant 2 in order to give the compiler complete
information about the proper arithmetic to use. Notice that this
constant is used in a context that expects an expression of type
s64 (64 bits, signed).

The expression 2 * (clock_rate - abs_nco_freq) is currently being
evaluated using 32-bit arithmetic.

Addresses-Coverity-ID: 1446589 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>