fastboot: Fix fastboot_vendor_boot_img_utils_test mac os compilation

Use more universal lseek instead of lseek64

Test: atest fastboot_vendor_boot_img_utils_test
Test: mm on mac os
Bug: 271152365
Change-Id: I4d094dd2c24e4ffec8ea7fe2f3b355122fd8cd19
Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>