spirv: only consider IO variables when adjusting patch locations for TES

With TES, the primitive ID is an input variable but it's considered a
sysval by SPIRV->NIR. Though, its value is greater than
VARYING_SLOT_VAR0 which means its location was adjusted by mistake.

This fixes compiling a tessellation evaluation shader in debug build
with Enshrouded.

Fixes: dfbc03fa88 ("spirv: Fix locations for per-patch varyings")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27413>

src/compiler/spirv/vtn_variables.c

@@ -2044,7 +2044,9 @@ adjust_patch_locations(struct vtn_builder *b, struct vtn_variable *var)
 
    for (uint16_t i = 0; i < num_data; i++) {
       vtn_assert(data[i].location < VARYING_SLOT_PATCH0);
-      if (data[i].patch && data[i].location >= VARYING_SLOT_VAR0)
+      if (data[i].patch &&
+          (data[i].mode == nir_var_shader_in || data[i].mode == nir_var_shader_out) &&
+          data[i].location >= VARYING_SLOT_VAR0)
          data[i].location += VARYING_SLOT_PATCH0 - VARYING_SLOT_VAR0;
    }
 }