fm10k: avoid possible truncation of q_vector->name

New versions of GCC since version 7 began warning about possible
truncation of calls to snprintf. We can fix this and avoid false
positives. First, we should pass the full buffer size to snprintf,
because it guarantees a NULL character as part of its passed length, so
passing len-1 is simply wasting a byte of possible storage.

Second, if we make the ri and ti variables unsigned, the compiler is
able to correctly reason that the value never gets larger than 256, so
it doesn't need to warn about the full space required to print a signed
integer.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>