staging: gdm7240: alloc_mux_rx() does not need GFP_ATOMIC

As far as alloc_mux_rx() is called from probe() only
there is no need in GFP_ATOMIC here.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>