usb: gadget: u_ether: reorganize code for better readability

Remove unnecessary else portion. Move code around to reduce
the number of spin_lock/unlock.

Change-Id: I614e4cacb279adfa67a6264e09b27c514a872306
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>
Signed-off-by: Sivasri Kumar Vanka <sivasri@codeaurora.org>