dma-debug: skip debug_dma_assert_idle() when disabled

If dma-debug is disabled due to a memory error, DMA unmaps do not affect
the dma_active_cacheline radix tree anymore, and debug_dma_assert_idle()
can print false warnings.

Disable debug_dma_assert_idle() when dma_debug_disabled() is true.

Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Fixes: 0abdd7a8 ("dma-debug: introduce debug_dma_assert_idle()")
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: James Bottomley <JBottomley@Parallels.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Horia Geanta <horia.geanta@freescale.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>