scsi: bfa: remove VLA

In preparation to enabling -Wvla, remove VLAs and replace them with
fixed-length arrays instead.

bfad_bsg.c uses a variable-length array declaration to measure the
size of a putative array; this can be replaced by the product of the
size of an element and the number of elements, avoiding the VLA
altogether.

This was prompted by https://lkml.org/lkml/2018/3/7/621



Signed-off-by: Stephen Kitt <steve@sk2.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>