disk: efi: avoid unaligned pointer error

disk: efi: avoid unaligned pointer error

When building with GCC 9.1 an error occurs:

disk/part_efi.c: In function ‘gpt_verify_partitions’:
disk/part_efi.c:737:49: error: taking address of packed member of
‘struct _gpt_entry’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  737 |   gpt_convert_efi_name_to_char(efi_str, gpt_e[i].partition_name,
      |                                         ~~~~~~~~^~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[1]: *** [scripts/Makefile.build:279: disk/part_efi.o] Error 1
make: *** [Makefile:1594: disk] Error 2

Adjust gpt_convert_efi_name_to_char() to accept unaligned strings.

Reported-by: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>