cpufreq: armada-37xx: use max() to calculate target_vm

cpufreq: armada-37xx: use max() to calculate target_vm

Use max() macro while calculating target_vm to simplify and improve the
armada-37xx-cpufreq driver code.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202503251256.rrl65HgY-lkp@intel.com/
Reported-by: Yang Ruibin <11162571@vivo.com>
Closes: https://lore.kernel.org/lkml/2c55fb07-b29e-43e0-8697-f75d1f0df89a@vivo.com/
Signed-off-by: Akhilesh Patil <akhilesh@ee.iitb.ac.in>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>