platform/x86: thinkpad_acpi: Take hotkey_mutex during hotkey_exit()

hotkey_exit() already takes the mutex around the hotkey_poll_stop_sync()
call, but not around the other calls.

commit 38831eaf ("platform/x86: thinkpad_acpi: use lockdep
annotations") has added lockdep_assert_held() checks to various hotkey
functions.

These lockdep_assert_held() checks fail causing WARN() backtraces in
dmesg due to missing locking in hotkey_exit(), fix this.

Fixes: 38831eaf ("platform/x86: thinkpad_acpi: use lockdep annotations")
Tested-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240424122834.19801-2-hdegoede@redhat.com

drivers/platform/x86/thinkpad_acpi.c

@@ -3044,10 +3044,9 @@ static void tpacpi_send_radiosw_update(void)
 
 static void hotkey_exit(void)
 {
-#ifdef CONFIG_THINKPAD_ACPI_HOTKEY_POLL
 	mutex_lock(&hotkey_mutex);
+#ifdef CONFIG_THINKPAD_ACPI_HOTKEY_POLL
 	hotkey_poll_stop_sync();
-	mutex_unlock(&hotkey_mutex);
 #endif
 	dbg_printk(TPACPI_DBG_EXIT | TPACPI_DBG_HKEY,
 		   "restoring original HKEY status and mask\n");
@@ -3057,6 +3056,8 @@ static void hotkey_exit(void)
 	      hotkey_mask_set(hotkey_orig_mask)) |
 	     hotkey_status_set(false)) != 0)
 		pr_err("failed to restore hot key mask to BIOS defaults\n");
+
+	mutex_unlock(&hotkey_mutex);
 }
 
 static void __init hotkey_unmap(const unsigned int scancode)