nandwrite: complain on malformed -s NUM

Elsewhere: use common error message. -30 bytes net size change

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/miscutils/nandwrite.c b/miscutils/nandwrite.c
index d0e4397..8df0fdc 100644
--- a/miscutils/nandwrite.c
+++ b/miscutils/nandwrite.c
@@ -72,6 +72,8 @@
 	xioctl(fd, MEMGETINFO, &meminfo);
 
 	mtdoffset = bb_strtou(opt_s, NULL, 0);
+	if (errno)
+		bb_error_msg_and_die("invalid number '%s'", opt_s);
 
 	/* Pull it into a CPU register (hopefully) - smaller code that way */
 	meminfo_writesize = meminfo.writesize;