USB: sierra: dma fixes

while I was adding autosuspend to that driver I noticed a few issues.
You were having DMAed buffers as a part of a structure.
This will fail on platforms that are not DMA-coherent (arm, sparc, ppc, ...)
Please test this patch to fix it.

Signed-off-by: Kevin Lloyd <klloyd@sierrawireless.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>