ACPI: EC: Limit burst to 64 bits

access_bit_width field is u8 in ACPICA, thus 256 value written to it
becomes 0, causing divide by zero later.

Proper fix would be to remove access_bit_width at all, just because
we already have access_byte_width, which is access_bit_width / 8.
Limit access width to 64 bit for now.

https://bugzilla.kernel.org/show_bug.cgi?id=15749
fixes regression caused by the fix for:
https://bugzilla.kernel.org/show_bug.cgi?id=14667



Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>