firmware: arm_scmi: Fix up turbo frequencies selection

Sustained frequency when greater than or equal to 4Ghz on 64-bit devices
currently result in marking all frequencies as turbo. Address the turbo
frequency selection bug by fixing the truncation.

Fixes: a897575e ("firmware: arm_scmi: Add support for marking certain frequencies as turbo")
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Message-Id: <20250514214719.203607-1-quic_sibis@quicinc.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>