mailbox: pcc: Fix an invalid-load caught by the address sanitizer

mainline inclusion
from mainline-v5.19-rc1
commit 369e4ef8
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6Z91B
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.3-rc2&id=369e4ef87a8f5da7c348ec2c61ec5cd726e8337a

--------------------------------

`pcc_mailbox_probe` doesn't initialize all memory that has been allocated
before the first time that one of it's members `txdone_irq` may be
accessed.

This leads to a an invalid load any time that this member is accessed:
[    2.429769] UBSAN: invalid-load in drivers/mailbox/pcc.c:684:22
[    2.430324] UBSAN: invalid-load in drivers/mailbox/mailbox.c:486:12
[    4.276782] UBSAN: invalid-load in drivers/acpi/cppc_acpi.c:314:45

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215587


Fixes: ce028702 ("mailbox: pcc: Move bulk of PCCT parsing into pcc_mbox_probe")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>