spi: aspeed: Replace VLA parameter with flat pointer in calibration helper

spi: aspeed: Replace VLA parameter with flat pointer in calibration helper

aspeed_spi_ast2600_optimized_timing() declared its buffer argument as a
variable-length array parameter (u8 buf[rows][cols]), which causes a
sparse warning. Replace the VLA parameter with a plain u8 * and compute
the 2-D index manually. The corresponding call site is also updated.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605180441.uD3toFRJ-lkp@intel.com/
Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Link: https://patch.msgid.link/20260522071621.102507-3-chin-ting_kuo@aspeedtech.com
Signed-off-by: Mark Brown <broonie@kernel.org>