meson: change vulkan icd config to - instead of _

Just to be consistent.

v2: - update meson.build too
v3: - remove unrelated whitespace change

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
diff --git a/meson.build b/meson.build
index 329495e..1e0b95f 100644
--- a/meson.build
+++ b/meson.build
@@ -22,7 +22,7 @@
         default_options : ['c_std=c99'])
 
 with_dri3 = true  # XXX: need a switch for this
-with_vulkan_icd_dir = get_option('vulkan_icd_dir')
+with_vulkan_icd_dir = get_option('vulkan-icd-dir')
 with_tests = get_option('build-tests')
 with_valgrind = get_option('valgrind')