ARM: mv78xx0: fix possible PCI buffer overflow

gcc-7.0 reports a potential array overflow:

arch/arm/mach-mv78xx0/pcie.c: In function 'mv78xx0_pcie_preinit':
arch/arm/mach-mv78xx0/pcie.c:81:4: error: output may be truncated before the last format character [-Werror=format-truncation=]

I haven't checked if this can actually happen, but making the
array one 32-bit word longer addresses the warning and makes
it completely safe.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>