firmware: qcom_scm: Fix error retval in __qcom_scm_is_call_available()

Since __qcom_scm_is_call_available() returns bool, have it return false
instead of -EINVAL if an invalid SMC convention is detected.

This fixes the Smatch static checker warning:

	drivers/firmware/qcom_scm.c:255 __qcom_scm_is_call_available()
	warn: signedness bug returning '(-22)'

Fixes: 9d11af8b ("firmware: qcom_scm: Make __qcom_scm_is_call_available() return bool")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Guru Das Srinagesh <quic_gurus@quicinc.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/1633982414-28347-1-git-send-email-quic_gurus@quicinc.com

drivers/firmware/qcom_scm.c

@@ -252,7 +252,7 @@ static bool __qcom_scm_is_call_available(struct device *dev, u32 svc_id,
 		break;
 	default:
 		pr_err("Unknown SMC convention being used\n");
-		return -EINVAL;
+		return false;
 	}
 
 	ret = qcom_scm_call(dev, &desc, &res);