powerpc/52xx: Fix a resource leak in an error handling path

The error handling path of mpc52xx_lpbfifo_probe() has a request_irq()
that is not balanced by a corresponding free_irq().

Add the missing call, as already done in the remove function.

Fixes: 3c9059d7 ("powerpc/5200: add LocalPlus bus FIFO device driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/dec1496d46ccd5311d0f6e9f9ca4238be11bf6a6.1643440531.git.christophe.jaillet@wanadoo.fr