isl/state: fix assert on raw buffer surface state minimum size

isl/state: fix assert on raw buffer surface state minimum size

From IVB PRM, SURFACE_STATE::Height:

"For typed buffer and structured buffer surfaces, the number of
 entries in the buffer ranges from 1 to 2^27 . For raw buffer
 surfaces, the number of entries in the buffer is the number of bytes
 which can range from 1 to 2^30."

The minimum value is 1, according to the spec. The spec quote
was already added into the code by 028f6d8317f00.

Fixes crashing tests under:

dEQP-VK.robustness.buffer_access.*

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>