m32r: make memset() global for CONFIG_KERNEL_BZIP2=y

Fix the m32r compile error:

  arch/m32r/boot/compressed/misc.c:31:14: error: static declaration of 'memset' follows non-static declaration
  make[5]: *** [arch/m32r/boot/compressed/misc.o] Error 1
  make[4]: *** [arch/m32r/boot/compressed/vmlinux] Error 2

by removing the static keyword.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>