arch/h8300: eliminate kgbd.c warning

Drop the "const" qualifier from arch_kgdb_ops to eliminate the gcc
warning (gcc version is 8.1.0).

arch/h8300/kernel/kgdb.c:132:24: error: conflicting type qualifiers for 'arch_kgdb_ops'
 const struct kgdb_arch arch_kgdb_ops = {
In file included from ../arch/h8300/kernel/kgdb.c:12:
../include/linux/kgdb.h:284:26: note: previous declaration of 'arch_kgdb_ops' was here
 extern struct kgdb_arch  arch_kgdb_ops;

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: uclinux-h8-devel@lists.sourceforge.jp
Signed-off-by: Yoshinori Sato <ysato@users.sourceforge.jp>