scons: Fix random_r check.

Fixes: 597bddad47e8 ("scons: Test for random_r()")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Matt Turner <mattst88@gmail.com>
diff --git a/scons/gallium.py b/scons/gallium.py
index f208c63..5834f6e 100755
--- a/scons/gallium.py
+++ b/scons/gallium.py
@@ -369,7 +369,7 @@
         if check_functions(env, ['strtod_l', 'strtof_l']):
             cppdefines += ['HAVE_STRTOD_L']
 
-        if check_functions(env, 'random_r'):
+        if check_functions(env, ['random_r']):
             cppdefines += ['HAVE_RANDOM_R']
 
         if check_functions(env, ['timespec_get']):