drm/radeon: Add missing "return false" after unmapping invalid BIOS

Without that, we would try to copy the unmapped BIOS.

Submitted by:	Christoph Mallon <christoph.mallon@gmx.de>
Approved by:	re (blanket)

sys/dev/drm2/radeon/radeon_bios.c

@@ -123,6 +123,7 @@ static bool radeon_read_bios(struct radeon_device *rdev)
 			    __func__, bios[0], bios[1]);
 		}
 		vga_pci_unmap_bios(vga_dev, bios);
+		return false;
 	}
 	rdev->bios = malloc(size, DRM_MEM_DRIVER, M_WAITOK);
 	memcpy(rdev->bios, bios, size);