ibmvnic: Fix IRQ mapping disposal in error path

RX queue IRQ mappings are disposed in both the TX IRQ and RX IRQ
error paths. Fix this and dispose of TX IRQ mappings correctly in
case of an error.

Fixes: ea22d51a ("ibmvnic: simplify and improve driver probe function")
Signed-off-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>