acpi: Fix gcc9 error -Waddress-of-packed-member

acpi: Fix gcc9 error -Waddress-of-packed-member

Simply adds the missing packed attribute to 'struct grub_acpi_madt'.

[  233s] ../../grub-core/commands/lsacpi.c: In function 'disp_acpi_xsdt_table':
[  233s] ../../grub-core/commands/lsacpi.c:201:27: error: converting a packed 'struct grub_acpi_table_header' pointer (alignment 1) to a 'struct grub_acpi_madt' pointer (alignment 4) may result in an unaligned pointer value [-Werror=address-of-packed-member]
[  233s]   201 |  disp_madt_table ((struct grub_acpi_madt *) t);
[  233s]       |                           ^~~~~~~~~~~~~~
[  233s] In file included from ../../grub-core/commands/lsacpi.c:23:
[  233s] ../../include/grub/acpi.h:50:8: note: defined here
[  233s]    50 | struct grub_acpi_table_header
[  233s]       |        ^~~~~~~~~~~~~~~~~~~~~~
[  233s] ../../include/grub/acpi.h:90:8: note: defined here
[  233s]    90 | struct grub_acpi_madt
[  233s]       |        ^~~~~~~~~~~~~~
[  233s] ../../grub-core/commands/lsacpi.c: In function 'disp_acpi_rsdt_table':
[  233s] ../../grub-core/commands/lsacpi.c:225:27: error: converting a packed 'struct grub_acpi_table_header' pointer (alignment 1) to a 'struct grub_acpi_madt' pointer (alignment 4) may result in an unaligned pointer value [-Werror=address-of-packed-member]
[  233s]   225 |  disp_madt_table ((struct grub_acpi_madt *) t);
[  233s]       |                           ^~~~~~~~~~~~~~
[  233s] In file included from ../../grub-core/commands/lsacpi.c:23:
[  233s] ../../include/grub/acpi.h:50:8: note: defined here
[  233s]    50 | struct grub_acpi_table_header
[  233s]       |        ^~~~~~~~~~~~~~~~~~~~~~
[  233s] ../../include/grub/acpi.h:90:8: note: defined here
[  233s]    90 | struct grub_acpi_madt
[  233s]       |        ^~~~~~~~~~~~~~

Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>