fixed a typo

Author: chrisgorgo

nipype/workflows/dmri/fsl/epi.py

@@ -655,7 +655,7 @@ def _compute_dwelltime(dwell_time=0.68, pi_factor=1.0, is_reverse_encoding=False
     return dwell_time
 
 def _effective_echospacing( dwell_time, pi_factor=1.0 ):
-    dwelltime = 1.0e-3 * dwelltime * ( 1.0/pi_factor )
+    dwelltime = 1.0e-3 * dwell_time * ( 1.0/pi_factor )
     return dwelltime