KVM: arm64: Fix potential leak in hyp_trace_buffer_alloc_bpages_backing

KVM: arm64: Fix potential leak in hyp_trace_buffer_alloc_bpages_backing

In the very unlikely event of a failure in __map_hyp, the allocated
backing pages are leaked in hyp_trace_buffer_alloc_bpages_backing(). Fix
this by freeing the pages on error.

Fixes: 3aed038aac8d ("KVM: arm64: Add trace remote for the nVHE/pKVM hyp")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260710114819.2689386-2-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>