Cortex-A76: fix spelling

Change-Id: I6adf7c14e8a974a7d40d51615b5e69eab1a7436f
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>

lib/cpus/aarch64/cortex_a76.S

@@ -22,7 +22,7 @@
 
 	/*
 	 * This macro applies the mitigation for CVE-2018-3639.
-	 * It implements a fash path where `SMCCC_ARCH_WORKAROUND_2`
+	 * It implements a fast path where `SMCCC_ARCH_WORKAROUND_2`
 	 * SMC calls from a lower EL running in AArch32 or AArch64
 	 * will go through the fast and return early.
 	 *