Kind of revert "powerpc: 52xx: provide a default in mpc52xx_irqhost_map()"

This more or less reverts commit 6391f697.
Instead of adding an unneeded 'default', mark the variable to prevent
the false positive 'uninitialized var'. The other change (fixing the
printout) needs revert, too. We want to know WHICH critical irq failed,
not which level it had.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Anatolij Gustschin <agust@denx.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>