wil6210: Block write ioctl to the card by default

The ability to write to the card is used for debug purposes.
The ability is disabled by default to prevent misuse of
this functionality.

CRs-Fixed: 1096945
Change-Id: I8fc3f646a0127ec705239be6a7de858a4f805acc
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>