Use generic/dot.c for DSDOT on ARMV5 and above

The default arm/dot.c is less precise when used for DSDOT, as shown by utest

kernel/arm/KERNEL.ARMV5

@@ -49,6 +49,7 @@ SDOTKERNEL   = ../arm/dot.c
 DDOTKERNEL   = ../arm/dot.c
 CDOTKERNEL   = ../arm/zdot.c
 ZDOTKERNEL   = ../arm/zdot.c
+DSDOTKERNEL  = ../generic/dot.c
 
 SNRM2KERNEL  = ../arm/nrm2.c
 DNRM2KERNEL  = ../arm/nrm2.c