libpldmresponder: Fix get the index of BIOSAttribute class
libpldmresponder: Fix get the index of BIOSAttribute class

`%` should be used instead of `/` to get the correct BIOSAttribute class.

Tested: test with JSON
https://gist.github.com/lxwinspur/2afffff2e445fddf90dfed6eceef4014

busctl get-property xyz.openbmc_project.BIOSConfigManager
/xyz/openbmc_project/bios_config/manager xyz.openbmc_project.BIOSConfig.Manager
BaseBIOSTable

a{s(sbsssvva(sv))} 5
"CodeUpdatePolicy"
"xyz.openbmc_project.BIOSConfig.Manager.AttributeType.Enumeration"
true "" "" "" s "Concurrent" s "Concurrent" 2
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.OneOf" s "Concurrent"
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.OneOf" s "Disruptive"

"Led"
"xyz.openbmc_project.BIOSConfig.Manager.AttributeType.Enumeration"
false "" "" "" s "Off" s "Off" 2
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.OneOf" s "On"
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.OneOf" s "Off"

"Model"
"xyz.openbmc_project.BIOSConfig.Manager.AttributeType.String"
false "" "" "" s "powersupply0" s "FP5280G2" 2
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.MinStringLength" x 1
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.MaxStringLength" x 100

"OUTLET"
"xyz.openbmc_project.BIOSConfig.Manager.AttributeType.Integer"
false "" "" "" x 9149282306036291456 x 0 3
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.LowerBound" x 0
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.UpperBound" x 68002
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.ScalarIncrement" x 1

"str_example3"
"xyz.openbmc_project.BIOSConfig.Manager.AttributeType.String"
true "" "" "" s "ef" s "ef" 2
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.MinStringLength" x 1
"xyz.openbmc_project.BIOSConfig.Manager.BoundType.MaxStringLength" x 100

Signed-off-by: George Liu <f124e69123cb985598dfa856ba74cb3263194267@inspur.com>
Change-Id: I4c5e61d54e7f4a1f4a99f0f987fefe12faae3034

openbmc/pldm,openbmc/pldm,openbmc/pldm