sbi: tlb: Simplify to tlb_process_count/tlb_process function

tlb_process_count is only used when count=1, so refactor to
tlb_process_once and add the return value to be reused in
tlb_process

Signed-off-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Tested-by: Anup Patel <anup@brainfault.org>