usb: dwc: using atomic kzalloc

The function msm_ep_config() can be called from an
interrupt context. As such, must use the GFP_ATOMIC
flag when allocating memory.

Change-Id: I55e85fa703b7c0086a91d97f3f01adbba8e5d2fc
Signed-off-by: Dov Levenglick <dovl@codeaurora.org>