Introduce changes recommended in the kernel mailing list

[teackot]

• use sysfs_emit() instead of sprintf() to prevent buffer overflow
• remove unnecessary ACPI check
• make i and len in ec_read_seq() the same type
• better error handling
• use pr_fmt for convenience

[teackot]

When this gets merged, I'll also send it to LKML

[BeardOverflow]

I reviewed each commit and looks good. Thanks for your constant effort!