tcl/target/eos_s3: fix variable's expansion typo

tcl/target/eos_s3: fix variable's expansion typo

TCL expands the variables only if preceded by a dollar sign.

Add the missing dollar before the variable's name '_CPUTAPID'.

Change-Id: Icc5d0dddf24f75d12ee63fee69e1b265e842ca43
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reported-by: Wes Cilldhaire <wes@sol1.com.au>
Fixes: c3166b43e415 ("tcl/target: Add QuickLogic EOS S3 MCU configuration")
Reviewed-on: http://openocd.zylin.com/6079
Tested-by: jenkins
Reviewed-by: TM <tommy_murphy@hotmail.com>