kselftest/arm64: Fix check_user_mem test

The check_user_mem test reports the error below because the test
plan is not declared correctly:

# Planned tests != run tests (0 != 4)

Fix the test adding the correct test plan declaration.

Fixes: 4dafc08d0ba4 ("kselftest/arm64: Check mte tagged user address in kernel")
Signed-off-by: Vincenzo Frascino <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Gabor Kertesz <[e-mail]>
Cc: Amit Daniel Kachhap <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

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

···
 	err = mte_default_setup();
 	if (err)
 		return err;
+
 	/* Register signal handlers */
 	mte_register_signal(SIGSEGV, mte_default_handler);
+
+	/* Set test plan */
+	ksft_set_plan(4);
 
 	evaluate_test(check_usermem_access_fault(USE_MMAP, MTE_SYNC_ERR, MAP_PRIVATE),
 		"Check memory access from kernel in sync mode, private mapping and mmap memory\n");