configure: Make indentation consistenly use tabs

We don't have enforcement for bash scripts, so of course
this ended up with mixed tabs and spaces.

Change-Id: Ideba6cdffa0687a40851a5cda6216a13f870a9ba
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/447242


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>