riscv: traps: Fix no prototype warnings

Fix all W=1 compilation warnings:'no previous prototype for' in arch/riscv/kernel/traps.c:
arch/riscv/kernel/traps.c:96:15: warning: no previous prototype for ‘do_trap_unknown’ [-Wmissing-prototypes]
   96 | DO_ERROR_INFO(do_trap_unknown,
      |               ^~~~~~~~~~~~~~~
arch/riscv/kernel/traps.c:91:27: note: in definition of macro ‘DO_ERROR_INFO’
   91 | asmlinkage __visible void name(struct pt_regs *regs)   \
      |                           ^~~~
arch/riscv/kernel/traps.c:98:15: warning: no previous prototype for ‘do_trap_insn_misaligned’ [-Wmissing-prototypes]
   98 | DO_ERROR_INFO(do_trap_insn_misaligned,
      |               ^~~~~~~~~~~~~~~~~~~~~~~
arch/riscv/kernel/traps.c:91:27: note: in definition of macro ‘DO_ERROR_INFO’
   91 | asmlinkage __visible void name(struct pt_regs *regs)   \
      |                           ^~~~
arch/riscv/kernel/traps.c:100:15: warning: no previous prototype for ‘do_trap_insn_fault’ [-Wmissing-prototypes]
...

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Nanyong Sun <sunnanyong@huawei.com>
[Palmer: fix checkpatch warnings]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>