alx: fix error handling in __alx_open

In commit 9ee7b683 we moved the enablement of msi interrupts earlier in
alx_init_intr. If there is an error in alx_alloc_rings, __alx_open returns
with an error but msi (or msi-x) interrupts stays enabled. Add a new error
label to disable msi (or msi-x) interrupts.

Fixes: 9ee7b683

 ("alx: refactor msi enablement and disablement")
Signed-off-by: Tobias Regnery <tobias.regnery@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>