platform/x86: panasonic-laptop: simplify allocation of sinf

platform/x86: panasonic-laptop: simplify allocation of sinf

Change to a flexible array member to allocate once instead of twice.

Use __counted_by for extra runtime analysis. Move the counting
variable assignment to right after allocation as done by
kzalloc_flex for GCC 15 and above.

Remove + 1 to allocation. It's already done in the previous line.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://patch.msgid.link/20260430221555.83351-1-rosenp@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>