storvsc: Set the error code correctly in failure conditions

In the function storvsc_channel_init(), error code was not getting
set correctly in some of the failure cases. Fix this issue.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>