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>