USB: gadget: function: fix issue Unneeded variable: "value"

fix below issue reported by coccicheck
drivers/usb/gadget/function/f_eem.c:169:7-12: Unneeded variable:
"value". Return "- EOPNOTSUPP" on line 179

We can not change return type of eem_setup as its registered with callback
function

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>