meson: fix regression finding shm dep

Just copy the dep into both places.

Fixes: b5c390c113 ("vulkan/wsi: add support for detecting mit-shm pixmaps.")
Reviewed-by: Adam Jackson <ajax@redhat.com>
Tested-by: Zoltán Böszörményi <zboszor@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12635>

meson.build

@@ -1963,6 +1963,7 @@ if with_platform_x11
     dep_xext = dependency('xext')
     dep_xfixes = dependency('xfixes', version : '>= 2.0')
     dep_xcb_glx = dependency('xcb-glx', version : '>= 1.8.1')
+    dep_xcb_shm = dependency('xcb-shm')
   endif
   if (with_any_vk or with_glx == 'dri' or with_egl or
        (with_gallium_vdpau or with_gallium_xvmc or with_gallium_va or