ANDROID: KVM: arm64: Fix missing null char for trace_hyp_printk()

In the event of a string format whos size is equal to the max, there
would be no string terminator. Enforce one.

While at it, bump the maximum size from 63 to 127. This is a debug
feature which won't consume any resources on a production kernel anyway.

Bug: 278749606
Change-Id: Ic56a61225a08760cac7ddaec1b712cbf652553c6
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>