x86: acpi: Add memset to initialize SPCR table

Add a missing memset to acpi_create_spcr().

The other acpi_create_xxxx() functions perform a memset on their
structures, acpi_create_spcr() does not and as a result the contents of
this table are partly uninitialized (and thus random after every reset).

Fixes: b288cd96 ("x86: acpi: Generate SPCR table")
Signed-off-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: fix the tags format in the commit message]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>