mfd/vexpress: vexpress_sysreg_setup must not be __init

The patch 52666298a 'mfd: vexpress-sysreg: Don't skip initialization
on probe' adds a call to vexpress_sysreg_setup from a non-__init
function, so this also has to lose its __init annotation.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: arm@kernel.org
Signed-off-by: Olof Johansson <olof@lixom.net>