sfio: correct misleading indentation in GETDISCF macro definition

sfio: correct misleading indentation in GETDISCF macro definition

Fixes errors like this when building with CMake (which uses -Wall,
-Wextra and -Werror) on Ubuntu 21.10 with gcc 11.2.0.

../lib/sfio/sfdisc.c:68:11: error: this ‘for’ clause does not guard... [-Werror=misleading-indentation]
   68 |         { for(d = f->disc; d && !d->iof; d = d->disc) ; \
      |           ^~~
../lib/sfio/sfdisc.c:71:5: note: in expansion of macro ‘GETDISCF’
   71 |     GETDISCF(oreadf, readf, Sfread_f);
      |     ^~~~~~~~
../lib/sfio/sfdisc.c:71:14: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
   71 |     GETDISCF(oreadf, readf, Sfread_f);
      |              ^~~~~~
../lib/sfio/sfdisc.c:69:11: note: in definition of macro ‘GETDISCF’
   69 |           func = d ? d->iof : NULL; \
      |           ^~~~