usb: gadget: f_hid: use alloc_ep_req()

Use gadget's framework allocation function instead of directly calling
usb_ep_alloc_request().

Change-Id: I247b0d325f553a1cb363f35def2b1aa4c0385dd0
Signed-off-by: Felipe F. Tonello <eu@felipetonello.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Git-commit: ba1582f22231821c57534e87b077d84adbc15dbd
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git


Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>