hw/i386: Fix compiler warning when CONFIG_IDE_ISA is disabled

hw/i386: Fix compiler warning when CONFIG_IDE_ISA is disabled

When CONFIG_IDE_ISA is disabled, compilation currently fails:

 hw/i386/pc_piix.c: In function ‘pc_init1’:
 hw/i386/pc_piix.c:81:9: error: unused variable ‘i’ [-Werror=unused-variable]

Move the variable declaration to the right code block to avoid
this problem.

Fixes: 4501d317b50e ("hw/i386/pc: Extract pc_i8259_create()")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20191115145049.26868-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>