ARM: 9276/1: Refactor dump_instr()

1. Rename local variable 'val16' to 'tmp'. So that the processing
   statements of thumb and arm can be aligned.
2. Fix two sparse check warnings: (add __user for type conversion)
   warning: incorrect type in initializer (different address spaces)
      expected unsigned short [noderef] __user *register __p
      got unsigned short [usertype] *
3. Prepare for the next patch to avoid repeated judgment.
   Before:
   if (!user_mode(regs)) {
           if (thumb)
           else
   } else {
           if (thumb)
           else
   }

   After:
   if (thumb) {
           if (user_mode(regs))
           else
   } else {
           if (user_mode(regs))
           else
   }

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>