kconfig: fix broken dependency in randconfig-generated .config

Running randconfig on arm64 using KCONFIG_SEED=0x40C5E904 (e.g. on v5.5)
produces the .config with CONFIG_EFI=y and CONFIG_CPU_BIG_ENDIAN=y,
which does not meet the !CONFIG_CPU_BIG_ENDIAN dependency.

This is because the user choice for CONFIG_CPU_LITTLE_ENDIAN vs
CONFIG_CPU_BIG_ENDIAN is set by randomize_choice_values() after the
value of CONFIG_EFI is calculated.

When this happens, the has_changed flag should be set.

Currently, it takes the result from the last iteration. It should
accumulate all the results of the loop.

Fixes: 3b9a19e0 ("kconfig: loop as long as we changed some symbols in randconfig")
Reported-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>