fix invalid buffer bind size in KHR-GL46.sparse_buffer_tests.BufferStorageTest

fix invalid buffer bind size in KHR-GL46.sparse_buffer_tests.BufferStorageTest

m_sparse_bo_data_size is the size of the sparse data, but this may exceed
the value returned by GL_MAX_UNIFORM_BLOCK_SIZE, which (should) cause
the test to fail on any driver where the sparse data size is larger than
the max uniform block size

instead, use the size of the data being passed to the shaders directly
so that this can never be too large

Affects:
KHR-GL46.sparse_buffer_tests.BufferStorageTest

Components: OpenGL
VK-GL-CTS Issue: 3468

Change-Id: Ie9d3de5760773e9b1b3b24e8af77976e7a54036c