tools: mkimage: fix sizeof_mismatch found by coverity

Reported-by: Coverity (CID: 155214)
Signed-off-by: Sven Ebenfeld <sven.ebenfeld@gmail.com>

tools/mkimage.c

@@ -526,7 +526,7 @@ int main(int argc, char **argv)
 							+ 0x20, 0 };
 			int i = params.file_size;
 			for (; i < aligned_filesize; i++) {
-				if (write(ifd, &i, 1) != 1) {
+				if (write(ifd, (char *) &i, 1) != 1) {
 					fprintf(stderr,
 							"%s: Write error on %s: %s\n",
 							params.cmdname,