[AArch64] Fix off-by-one when calculating tag granules.

When we want to fetch tags from a memory range, the last address in that
range is not included.

There is a off-by-one error in aarch64_mte_get_tag_granules, which this
patch fixes.

gdb/ChangeLog:

2021-05-13  Luis Machado  <luis.machado@linaro.org>

	* arch/aarch64-mte-linux.c (aarch64_mte_get_tag_granules): Don't
	include the last address in the range.