glsl: fix GL_BUFFER_DATA_SIZE value for shader storage blocks with unsize arrays

glsl: fix GL_BUFFER_DATA_SIZE value for shader storage blocks with unsize arrays

From ARB_program_interface_query:

"For the property of BUFFER_DATA_SIZE, then the implementation-dependent
 minimum total buffer object size, in basic machine units, required to hold
 all active variables associated with an active uniform block, shader
 storage block, or atomic counter buffer is written to <params>.  If the
 final member of an active shader storage block is array with no declared
 size, the minimum buffer size is computed assuming the array was declared
 as an array with one element."

Fixes the following dEQP-GLES31 tests:

dEQP-GLES31.functional.program_interface_query.shader_storage_block.buffer_data_size.named_block
dEQP-GLES31.functional.program_interface_query.shader_storage_block.buffer_data_size.unnamed_block
dEQP-GLES31.functional.program_interface_query.shader_storage_block.buffer_data_size.block_array

v2:
- Fix comment's indentation and explain that the parser already
  checked that unsized array is in last element of a shader
  storage block (Iago).
- Add assert (Iago).

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>