usb: gadget: make snd_pcm_hardware const

Make this const as it is only used during a copy operation.
Done using Coccinelle.

Change-Id: I91203bd925841c0795289590aca5252eaeb289ea
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: 2ab3c34c9c75331143d67042e826bdcde4d6ab37
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git


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