arm64: mte: style: Simplify bool comparison

Fix the following coccicheck warning:
./tools/testing/selftests/arm64/mte/check_buffer_fill.c:84:12-35:
WARNING: Comparison to bool
Signed-off-by: YANG LI <abaci-bugfix@linux.alibaba.com>
Reported-by: Abaci Robot<abaci@linux.alibaba.com>
Link: https://lore.kernel.org/r/1610357737-68678-1-git-send-email-abaci-bugfix@linux.alibaba.comSigned-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/mte/check_buffer_fill.c

@@ -81,7 +81,7 @@ static int check_buffer_underflow_by_byte(int mem_type, int mode,
 		last_index = 0;
 		/* Set some value in tagged memory and make the buffer underflow */
 		for (j = sizes[i] - 1; (j >= -underflow_range) &&
-				       (cur_mte_cxt.fault_valid == false); j--) {
+				       (!cur_mte_cxt.fault_valid); j--) {
 			ptr[j] = '1';
 			last_index = j;
 		}