Handle channel IDs without index or modifier correctly
Handle channel IDs without index or modifier correctly

Channel whose ID is "timestamp" has type IIO_CHAN_TYPE_UNKNOWN
before this patch, but it should be IIO_TIMESTAMP.

Signed-off-by: Ryo Hashimoto <7ea00519fdb4bf6e413a65300cdb4cc81913fc76@google.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio