gsm-inhibit-dialog: Fix -Wimplicit-int-float-conversion warnings

[rbuj]

gsm-inhibit-dialog.c:311:38: warning: implicit conversion from 'int' to 'float' may lose precision [-Wimplicit-int-float-conversion]
                int scale_x = (int) (pw * scale_factor);
                                     ^~ ~
---
gsm-inhibit-dialog.c:312:38: warning: implicit conversion from 'int' to 'float' may lose precision [-Wimplicit-int-float-conversion]
                int scale_y = (int) (ph * scale_factor);
                                     ^~ ~

[raveit65]

LGTM,
warning is gone, tested and application runs well.

[zhuyaliang]

Warning fixed