meson: Fix with_gallium_icd to with_opencl_icd

`with_gallium_icd` is never used throughout the different Meson build
files, whereas `with_opencl_icd` tracks whether or not `gallium-opencl`
was set to "icd".

Fixes: 42ea0631f1
         ("meson: build clover")
Signed-off-by: Pierre Moreau <pierre.morrow@free.fr>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

meson.build

@@ -668,7 +668,7 @@ if _opencl != 'disabled'
 else
   dep_clc = null_dep
   with_gallium_opencl = false
-  with_gallium_icd = false
+  with_opencl_icd = false
 endif
 
 gl_pkgconfig_c_flags = []