x86/pmem: Fix platform-device leak in error path

Make sure to free the platform device in the unlikely event that
registration fails.

Fixes: 7a67832c7e44 ("libnvdimm, e820: make CONFIG_X86_PMEM_LEGACY a tristate option")
Signed-off-by: Johan Hovold <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/kernel/pmem.c

···
 	 * simply here to trigger the module to load on demand.
 	 */
 	pdev = platform_device_alloc("e820_pmem", -1);
-	return platform_device_add(pdev);
+
+	rc = platform_device_add(pdev);
+	if (rc)
+		platform_device_put(pdev);
+
+	return rc;
 }
 device_initcall(register_e820_pmem);