cosmetic: comment spelling

Change-Id: I89e2ae1478688929a42c94c8279ebff1b3a6cd88
diff --git a/firmware/ice40-riscv/icE1usb/usb_e1.c b/firmware/ice40-riscv/icE1usb/usb_e1.c
index ff58c08..dafceb5 100644
--- a/firmware/ice40-riscv/icE1usb/usb_e1.c
+++ b/firmware/ice40-riscv/icE1usb/usb_e1.c
@@ -40,7 +40,7 @@
 	uint32_t val = 8192;
 	unsigned int level;
 
-	/* Compute real E1 tick count (with safety agains bad values) */
+	/* Compute real E1 tick count (with safety against bad values) */
 	ticks = e1_tick_read();
 	val = (ticks - ticks_prev) & 0xffff;
 	ticks_prev = ticks;