staging: csr: remove panic at locking the mutex

when down_interruptible fail, means a signal occur, or any other failure
we are panicing, and it seems that we should not panic, instead we would
have done a spinlock, but currently removing the panic call.

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>