ANDROID: arm64: Fix the address of ftrace_call compiled with CFI_CLANG

When CONFIG_CFI_CLANG and CONFIG_DYNAMIC_FTRACE are enabled, LLVM will
generate a jump function named ftrace_call.cfi_jt for ftrace_call, which
makes "&ftrace_call" in ftrace_update_ftrace_func() actually the address
of ftrace_call.cfi_jt. As a result, the tracer can't be really enabled
through runtime modification. Use __va_function() to get the actual address
of ftrace_call to fix the issue.

Bug: 184105181
Signed-off-by: Ben Dai <ben.dai@unisoc.com>
Change-Id: Ic9272cd4ab447b3b145d8e397e5c9010c49f7a12