ARM: UniPhier: fix IECTRL set code for PH1-Pro4

For PH1-Pro4, the bit 6 of the IECTRL must be set.  It is the only
available bit in this register.  There is no effect of the write
access to the other bits.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>