LibC+Kernel: Switch off_t to 64 bits

Author: https://github.com/boricj
Commit: 7a079f7780
Pull-request: https://github.com/SerenityOS/serenity/pull/5766
Reviewed-by: https://github.com/supercomputer7

Kernel/API/Syscall.h

@@ -244,7 +244,7 @@ struct SC_mmap_params {
     int32_t prot;
     int32_t flags;
     int32_t fd;
-    ssize_t offset;
+    int64_t offset;
     StringArgument name;
 };