x86/mcelog: Add compat_ioctl for 32-bit mcelog support

A 32-bit version of mcelog issuing ioctls on /dev/mcelog causes errors
like the following:

  MCE_GET_RECORD_LEN: Inappropriate ioctl for device

This is due to a missing compat_ioctl callback.

Assign to it compat_ptr_ioctl() as a generic implementation of the
.compat_ioctl file operation to ioctl functions that either ignore the
argument or pass a pointer to a compatible data type.

 [ bp: Massage commit message. ]
Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/1583303947-49858-1-git-send-email-zhe.he@windriver.com

arch/x86/kernel/cpu/mce/dev-mcelog.c

@@ -329,6 +329,7 @@ static const struct file_operations mce_chrdev_ops = {
 	.write			= mce_chrdev_write,
 	.poll			= mce_chrdev_poll,
 	.unlocked_ioctl		= mce_chrdev_ioctl,
+	.compat_ioctl		= compat_ptr_ioctl,
 	.llseek			= no_llseek,
 };