powerpc/reg.h: delete duplicated word

Drop the repeated word "a".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200726003809.20454-8-rdunlap@infradead.org

arch/powerpc/include/asm/reg.h

@@ -1479,7 +1479,7 @@ static inline void update_power8_hid0(unsigned long hid0)
 {
 	/*
 	 *  The HID0 update on Power8 should at the very least be
-	 *  preceded by a a SYNC instruction followed by an ISYNC
+	 *  preceded by a SYNC instruction followed by an ISYNC
 	 *  instruction
 	 */
 	asm volatile("sync; mtspr %0,%1; isync":: "i"(SPRN_HID0), "r"(hid0));