Added check for DMA mapping errors for request sense data
buffer. Checking for mapping error can avoid potential wild
writes. This patch was prompted by the warning from
dma_unmap when kernel is compiled with CONFIG_DMA_API_DEBUG.
Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>