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