sh: kernel: traps: remove unused variable

sh: kernel: traps: remove unused variable

When building defconfig the following warning shows up:

arch/sh/kernel/traps.c: In function 'nmi_trap_handler':
arch/sh/kernel/traps.c:183:15: warning: unused variable 'cpu' [-Wunused-variable]
  unsigned int cpu = smp_processor_id();
               ^~~

Remove an unused variable 'cpu'.

Fixes: fe3f1d5d7cd3 ("sh: Get rid of nmi_count()")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Rich Felker <dalias@libc.org>