media: rtl2832: use 64-bit arithmetic instead of 32-bit in rtl2832_set_frontend

Add suffix ULL to constant 7 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
u64 (64 bits, unsigned).

The expression dev->pdata->clk * 7 is currently being evaluated
using 32-bit arithmetic.

Addresses-Coverity-ID: 1271223 ("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>