bfin_mac: fix error path

While building blackfin defconfig we were getting a build warning:
warning: label 'out_err_irq_alloc' defined but not used.

Commit e7f4dc35 ("mdio: Move allocation of interrupts into core")
removed the label out_err_mdiobus_register but then mistakenly jumped to
out_err_alloc. But it was actually supposed to jump to out_err_irq_alloc.

Fixes: e7f4dc35 ("mdio: Move allocation of interrupts into core")
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: David S. Miller <davem@davemloft.net>