ir_function_inlining: Fix missing iter.next() in inlining sampler params.

Fixes glsl-fs-function-samplers.
diff --git a/src/glsl/ir_function_inlining.cpp b/src/glsl/ir_function_inlining.cpp
index 35eb2b3..fd52d10 100644
--- a/src/glsl/ir_function_inlining.cpp
+++ b/src/glsl/ir_function_inlining.cpp
@@ -196,6 +196,8 @@
 	 assert(deref);
 	 do_sampler_replacement(&new_instructions, sig_param, deref);
       }
+      param_iter.next();
+      sig_param_iter.next();
    }
 
    /* Now push those new instructions in. */