package/zbar: needs c99 mode

package/zbar: needs c99 mode

Fixes [1]:

  bar/sqcode.c: In function 'sq_scan_shape':
  zbar/sqcode.c:171:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
       for (int x = x0 - 1; x < x0 + width + 1; x++) {
       ^
  zbar/sqcode.c:171:5: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code

[1] http://autobuild.buildroot.net/results/7d544275756f655f9d42c05562aca653923155b1

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>