xen/hvm: Don't skip MSR_READ trace record

Commit 37f074a338 ("x86/msr: introduce guest_rdmsr()") introduced a
function to combine the MSR_READ handling between PV and HVM.
Unfortunately, by returning directly, it skipped the trace generation,
leading to gaps in the trace record, as well as xenalyze errors like
this:

hvm_generic_postprocess: d2v0 Strange, exit 7c(VMEXIT_MSR) missing a handler

Replace the `return` with `goto out`.

Fixes: 37f074a338 ("x86/msr: introduce guest_rdmsr()")
Signed-off-by: George Dunlap <george.dunlap@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/hvm.c

@@ -3557,7 +3557,7 @@ int hvm_msr_read_intercept(unsigned int msr, uint64_t *msr_content)
     fixed_range_base = (uint64_t *)v->arch.hvm.mtrr.fixed_ranges;
 
     if ( (ret = guest_rdmsr(v, msr, msr_content)) != X86EMUL_UNHANDLEABLE )
-        return ret;
+        goto out;
 
     ret = X86EMUL_OKAY;