indent(1): Rearrange option parsing code to squelch clang's static analyzer.

clang-analyzer complained that eqin() sets file-scoped pointer param_start
to point into char buffer defined in scan_profile(), and once
scan_profile() exits, param_start is a "dangling reference". param_start
was never used afterwards, but it's cleaner to move it to set_option()
which is the only branch where param_start is needed.

Reference:
https://github.com/pstef/freebsd_indent/commit/ab0e44e5da3ff0fa4b62e451e4bbc3ea1ec7f365

Differential Revision: https://reviews.freebsd.org/D6966 (Partial)
Submitted by: Piotr Stefaniak