ARM: owl: smp: Use __pa_symbol()

Replace an occurrence of virt_to_phys() with __pa_symbol() macro.

See 64fc2a94 ("ARM: 8641/1: treewide:
Replace uses of virt_to_phys with __pa_symbol").

Fixes: 172067e0 ("ARM: owl: Implement CPU enable-method for S500")
Reported-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>