MLBEDSW-3890 handling scratch tensor

vela: Possible issue with handling scratch tensor on non-ethosu custom op

Fixing a case where a tensor input name ends with "scratch".
4 test cases passing this change:
1) non-optimized tflite - input tensor name is _split_1_scratch
2) optimized tflite - input tensor name is _split_1_scratch
3) optimized tflite - input tensor name is _split_1_scratch and custom
   operation name is non_ethus_u
4) non-optimized tflite - input tensor name is _split_1_scratch_fast

Change-Id: Ia515805825b7f9a646607c5075b7ea3a0cf6aad8
Signed-off-by: Samuel Panijel <samuel.panijel@arm.com>