Fix small error in HP_TIMING_PRINT trailing null char setting

Fix a small error in the HP_TIMING_PRINT trailing zero setting; the '\0'
should be set at MIN(Len,string length), instead of always at the 'Len'
position.

	* sysdeps/generic/hp-timing-common.h (HP_TIMING_PRINT): Correct
	position of string null termination.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>