mips32, write handler code in a more compact way

Less code and probably cleaner.
Don't check if it is ever ERROR_OK.

Change-Id: I1045b58fd4542ec24430332f49679364ae97b1dc
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/4018


Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>