[Blackfin] serial driver: Fix bug Free rx dma buffer in shutdown.
[Blackfin] serial driver: Fix bug Free rx dma buffer in shutdown.

Kernel crash for the serial driver in DMA mode:
http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=3679

Signed-off-by: Sonic Zhang <c93d368f28096020dd845c4879a931e9d13ab23f@analog.com>
Signed-off-by: Bryan Wu <465f0e91e61585f5bc1128e7fe63296c33a56926@analog.com>


TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs