Fix copy pasta error in handling of Z80 VDP port reads. HV counter reads are not illegal writes =P. Fixes immediate exit in Overdrive II, though other problems remain

#ifndef PPM_H_
#define PPM_H_

void save_ppm(FILE *f, uint32_t *buffer, uint32_t width, uint32_t height, uint32_t pitch);

#endif //PPM_H_