meson: Fix typo in clover build

The leading space breaks things.

fixes: 42ea0631f108d ("meson: build clover")
Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
diff --git a/meson.build b/meson.build
index cb8ec89..1a1d3fd 100644
--- a/meson.build
+++ b/meson.build
@@ -584,7 +584,7 @@
 endif
 
 _opencl = get_option('gallium-opencl')
-if _opencl !=' disabled'
+if _opencl != 'disabled'
   if not with_gallium
     error('OpenCL Clover implementation requires at least one gallium driver.')
   endif