dmaengine: idxd: check return result from check_vma() in cdev

dmaengine: idxd: check return result from check_vma() in cdev

The returned result from the check_vma() function in the cdev ->mmap() call
needs to be handled. Add the check and returning error.

Fixes: 42d279f9137a ("dmaengine: idxd: add char driver to expose submission portal to userland")
Reported-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/158264926659.9387.14325163515683047959.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>