Staging: bcm: Fix an invalid dereference to a kmalloc in IOCTL_BCM_BULK_WRM

Variable IoBuffer.InputLength is chosen from userspace,
and can therefore be less than the intended size. In this
case,the memory from the kmalloc call is eventually cast
to a PBULKWRM_BUFFER. If the IoBuffer.InputLength does not
meet the minimum size of PBULKWRM_BUFFER, then we will get
a kernel Oops. To resolve this issue, this patch verifies
IoBuffer.InputLength meets the minimum size before invoking
the kmalloc call.

Signed-off-by: Kevin McKinney <klmckinney1@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>