OMAP4: OTG: Fix compilation warning.

drivers/usb/otg/otg_id.c: In function '__otg_id_notify':
drivers/usb/otg/otg_id.c:47: warning: 'ret' may be used uninitialized in
this function

ret is initialized by OTG_ID_UNHANDLED

Change-Id: Ib8b408013dd9ea238071e63e709602326796afc5
Signed-off-by: Oleksandr Kozaruk <oleksandr.kozaruk@ti.com>