esrt: fix ESRT GUID for EFI device

[aokblast]

The EFI GUID in FreeBSD is layouted as following

typedef struct efi_guid { uint32_t Data1; uint16_t Data2; uint16_t Data3; uint8_t Data4[8]; } efi_guid_t;

Which means the Data1, Data2, Data3 should follows the little endian rule as the MSB should be in the right side.

Also, the table_len in the ioctl argument of EFI_GET_TABLE should be follow the uuid structure. Fix it by reorder it.