stm32lx_dual_bank.cfg: fix typo in file path

s/stm32l1x/stm32lx

...this makes tm32lx_dual_bank.cfg work again.

Change-Id: I04dc617523caa6b46c675fe9b700d1bbe88170e6
Signed-off-by: Andrey Yurovsky <yurovsky@gmail.com>
Reviewed-on: http://openocd.zylin.com/1832
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

tcl/target/stm32lx_dual_bank.cfg

@@ -2,7 +2,7 @@
 # Let's add a definition for the second bank here.
 
 # script for stm32lx family
-source [find target/stm32l1x_stlink.cfg]
+source [find target/stm32lx_stlink.cfg]
 
 # Add the second flash bank.
 set _FLASHNAME $_CHIPNAME.flash1