usb:f_midi:Correct the midi function name for binding

usb:f_midi:Correct the midi function name for binding

The f_midi function name has to be midi
Otherwise, the rc file will have problem of binding the function

Change-Id: I2b3e61f70fb9b260731eabd5fe6bf10da72c540a
Signed-off-by: a17671 <a17671@motorola.com>
Reviewed-on: https://gerrit.mot.com/1290747
SLTApproved: Slta Waiver
SME-Granted: SME Approvals Granted
Tested-by: Jira Key
Reviewed-by: Wei Deng <dengwei1@motorola.com>
Reviewed-by: Xiangpo Zhao <zhaoxp3@motorola.com>
Submit-Approved: Jira Key