cmd/compile: fix PPC64.rules to correct failure in issue45344.go with regabi

This changes a rule in PPC64.rules to fix a failure in
test/issue45344.go when regabi is enabled.

Change-Id: I98baf2ae92c766b7276b0f3167b2e6fef37dfe84
Reviewed-on: https://go-review.googlesource.com/c/go/+/353789
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Trust: Lynn Boger <laboger@linux.vnet.ibm.com>

Author: laboger

src/cmd/compile/internal/ssa/gen/PPC64.rules

@@ -580,7 +580,7 @@
 (Store {t} ptr val mem) && t.Size() == 8 && is64BitFloat(val.Type) => (FMOVDstore ptr val mem)
 (Store {t} ptr val mem) && t.Size() == 8 && is32BitFloat(val.Type) => (FMOVDstore ptr val mem) // glitch from (Cvt32Fto64F x) => x -- type is wrong
 (Store {t} ptr val mem) && t.Size() == 4 && is32BitFloat(val.Type) => (FMOVSstore ptr val mem)
-(Store {t} ptr val mem) && t.Size() == 8 && (is64BitInt(val.Type) || isPtr(val.Type)) => (MOVDstore ptr val mem)
+(Store {t} ptr val mem) && t.Size() == 8 && !is64BitFloat(val.Type) => (MOVDstore ptr val mem)
 (Store {t} ptr val mem) && t.Size() == 4 && is32BitInt(val.Type) => (MOVWstore ptr val mem)
 (Store {t} ptr val mem) && t.Size() == 2 => (MOVHstore ptr val mem)
 (Store {t} ptr val mem) && t.Size() == 1 => (MOVBstore ptr val mem)