Fix clang-tidy performance warnings in simpleperf.

* Use const reference type for parameters to avoid unnecessary copy.
* Use faster overloaded string find function.

Bug: 30407689
Bug: 30411878
Change-Id: I2dac3ab1928fd51fe03c4d7889f17f3b165918f3
Test: build with WITH_TIDY=1
1 file changed