at-spi-bus-launcher: fix parsing command line arguments
at-spi-bus-launcher: fix parsing command line arguments

Fix parsing --a11y=... and --screen-reader=...
sscanf returns the number of input items successfully matched,
and for one argument it is 1, but not 2.

https://bugzilla.gnome.org/show_bug.cgi?id=765220

GNOME/at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core