s/riscv/riscv64/

Unlike the kernel script (where plain "riscv" was correct because that's
what the kernel uses, making no distinction between riscv32 and riscv64
in the uapi header directories), this should say "riscv64" because
that's what our build system uses.

(This wasn't caught because we haven't wired up the .bp file yet.)

Test: treehugger
Change-Id: I086aaa89e69bf4ddc484a7e93a6c413fd8c719ff

tools/generate-version-script.py

@@ -8,7 +8,7 @@
 import sys
 
 def has_arch_tags(tags):
-  for arch in ["arm", "arm64", "riscv", "x86", "x86_64"]:
+  for arch in ["arm", "arm64", "riscv64", "x86", "x86_64"]:
     if arch in tags:
       return True
   return False