cppcheck warns that the format string is incorrect in the function
ixgbe_get_strings().  Since the value cannot be negative, change the
variable to unsigned which matches the format specifier.
Signed-off-by: NTony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>