fwk: Return a value from a non-void function

Some compilers complain the return type error as below.

 | arch/none/host/include/arch_helpers.h: In function ‘arch_interrupts_disable’:
 | arch/none/host/include/arch_helpers.h:25:1: error: no return statement in
 |	function returning non-void [-Werror=return-type]

Fix the same.

Change-Id: Ia3343fbbea57ae783b272f0c4db05a7060256f85
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>