Staging: bcm: Add size minimum size restrictions for IOCTL_IDLE_REQ

If IoBuffer.InputLength is zero then this will cause an Oops when
we dereference the ZERO_SIZE_PTR.  Or if it's smaller than
sizeof(struct link_request) then we would get memory corruption
when we set ->PLength in CopyBufferToControlPacket().

Signed-off-by: Kevin McKinney <klmckinney1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>