usb: host: ohci-st: Remove set but not used variable 'ohci'
Fixes gcc '-Wunused-but-set-variable' warning:
drivers/usb/host/ohci-st.c: In function st_ohci_platform_probe:
drivers/usb/host/ohci-st.c:135:19: warning: variable ohci set but not used [-Wunused-but-set-variable]