iommu/omap: Check for failure of a call to omap_iommu_dump_ctx

It is possible for the call to omap_iommu_dump_ctx to return
a negative error number, so check for the failure and return
the error number rather than pass the negative value to
simple_read_from_buffer.

Fixes: 14e0e6796a0d ("OMAP: iommu: add initial debugfs support")
Signed-off-by: Colin Ian King <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Addresses-Coverity: ("Improper use of negative value")
Signed-off-by: Joerg Roedel <[e-mail]>

drivers/iommu/omap-iommu-debug.c

···
 	mutex_lock(&iommu_debug_lock);
 
 	bytes = omap_iommu_dump_ctx(obj, p, count);
+	if (bytes < 0)
+		goto err;
 	bytes = simple_read_from_buffer(userbuf, count, ppos, buf, bytes);
 
+err:
 	mutex_unlock(&iommu_debug_lock);
 	kfree(buf);