USB:gadget:designware Device controller bugfixes

This patch fixes a few bugs in USB device controller driver.
The fixes are as follows
1. Adding error condition checks eg. NULL return
2. Endpoint other than endpoint 0 (control endpoint) are initialized
only if usb state machine reaches STATE_ADDRESSED or above
3. Zero length packet handling corrected
4. Dead code removed
5. Bulk out endpoint returns after servicing 1 interrupt and returns
back to service if more interrupts are pending

Signed-off-by: Vipin Kumar <vipin.kumar@st.com>
Signed-off-by: Amit Virdi <amit.virdi@st.com>
Acked-by: Marek Vasut <marex@denx.de>