ARM: UniPhier: remove unnecessary ifdef conditional

The callee (arch/arm/lib/cache-cp15.c) has a #ifdef
CONFIG_SYS_DCACHE_OFF conditional.  The same conditional in the
caller (arch/arm/mach-uniphier/cache_uniphier.c) is redundant.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>