benchdnn: inputs: graph: set fpmath mode for int4 mlp test

Author: TaoLv

tests/benchdnn/inputs/graph/complex_fusion/harness_mlp_ci

@@ -6,4 +6,4 @@
 --reset --in-shapes=0:1x128+1:128x256+4:128x256+13:256x128 --op-kind=12:Subtract --case=complex_fusion/mlp/gated-mlp-f32.json
 
 # f16-int4 case
---reset --case=complex_fusion/mlp/gated-mlp-int4.json
+--reset --attr-fpmath=f16:true --case=complex_fusion/mlp/gated-mlp-int4.json