i965/fs/nir: fix the number of register written by FS_OPCODE_GET_BUFFER_SIZE

FS_OPCODE_GET_BUFFER_SIZE is calculated with a resinfo's sampler message.

This patch adjusts the number of registers written by the opcode
following what the PRM spec says about the number of registers written
by the SIMD8 and SIMD16's writeback messages for sampler messages.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
1 file changed