greybus: connection: fix non-atomic allocations under spin lock

Use GFP_ATOMIC for IDA memory allocations under spin lock, which must
not sleep.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>