kselftest/arm64: mte: Fix clang warning

if (!prctl(...) == 0) is not only cumbersome to read, it also upsets
clang and triggers a warning:
------------
mte_common_util.c:287:6: warning: logical not is only applied to the
left hand side of this comparison [-Wlogical-not-parentheses]
....

Fix that by just comparing against "not 0" instead.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Mark Brown <broone@kernel.org>
Link: https://lore.kernel.org/r/20210319165334.29213-11-andre.przywara@arm.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

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

@@ -284,7 +284,7 @@ int mte_switch_mode(int mte_option, unsigned long incl_mask)
 
 	en |= (incl_mask << PR_MTE_TAG_SHIFT);
 	/* Enable address tagging ABI, mte error reporting mode and tag inclusion mask. */
-	if (!prctl(PR_SET_TAGGED_ADDR_CTRL, en, 0, 0, 0) == 0) {
+	if (prctl(PR_SET_TAGGED_ADDR_CTRL, en, 0, 0, 0) != 0) {
 		ksft_print_msg("FAIL:prctl PR_SET_TAGGED_ADDR_CTRL for mte mode\n");
 		return -EINVAL;
 	}