OvmfPkg/AcpiPlatformDxe: Use local variable in QemuFwCfgAcpi.c

OvmfPkg/AcpiPlatformDxe: Use local variable in QemuFwCfgAcpi.c

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4237

The handle of mQemuAcpiHandle is not needed for anything, beyond the
scope of the InstallQemuFwCfgTables(). So a local variable will
suffice for storing the handle.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Reported-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
Message-Id: <20230111012235.189-4-min.m.xu@intel.com>