toshiba_acpi: Initialize hotkey_event_type variable

Commit 53147b6c ("toshiba_acpi: Fix
hotkeys registration on some toshiba models") fixed an issue on some
laptops regarding hotkeys registration, however, if failed to address
the initialization of the hotkey_event_type variable, and thus, it can
lead to potential unwanted effects as the variable is being checked.

This patch initializes such variable to avoid such unwanted effects.

Cc: <stable@vger.kernel.org> # 4.1+
Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>