Staging: hv: storvsc: Cleanup error handling in storvsc_dev_add()

Use standard Linux error values and cleanup error handling. I would like
to acknowledge Andre Bartke (andre.bartke@gmail.com) for highlighting this
problem.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>