SF: Fix refresh rate selection for low physical refresh rates

With the render frame rate introduction of physical refresh rate
divisors, a hardcoded minimum frame rate was added. This minimum was
incorrectly applied to physical refresh rates in addition to divisors,
which prevented lower physical refresh rates to be enumarated.

Test: atest libsurfaceflinger_unittest
Bug: 261520501
Change-Id: I597f9c61bd7a0e8fd2dc16415e36d97c1417f74f