usb: gadget: composite: Add spinlock protection for usb config descriptor

During composition switch, android driver stops data transfers first and
removes configuration before disabling pullup for USB3 controller. With
this sequence there is a possibility for a race where usb_remove_config is
in progress during which pullup is active and sending the setup request for
configuration descriptor with zero configuration value. Hence fix the issue
by adding spinlock protection for get_config descriptor.

CRs-Fixed: 1052608
Change-Id: I65d38387f77addc9a8894a74f427d97313f90a9e
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>