st/mesa: add compiler/nir/ prefix for nir includes

Stay consistent with the rest of the codebase, effectively fixing the
autotools build.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105621
Fixes: ffa4bbe466 ("st/nir/radeonsi: move nir_lower_uniforms_to_ubo()
to the state tracker")
Cc: Timothy Arceri <tarceri@itsqueeze.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_nir_lower_uniforms_to_ubo.c

@@ -29,8 +29,8 @@
  * point by 1.
  */
 
-#include "nir.h"
-#include "nir_builder.h"
+#include "compiler/nir/nir.h"
+#include "compiler/nir/nir_builder.h"
 #include "st_nir.h"
 
 #include "program/prog_parameter.h"