Blackfin: add note about anomaly 05000242 being worked around

Document anomaly 05000242 workaround in source code.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/arch/blackfin/mach-common/clocks-init.c b/arch/blackfin/mach-common/clocks-init.c
index 3539365..ef6870e 100644
--- a/arch/blackfin/mach-common/clocks-init.c
+++ b/arch/blackfin/mach-common/clocks-init.c
@@ -72,6 +72,7 @@
 #endif
 	bfin_write_PLL_LOCKCNT(0x300);
 	do_sync();
+	/* We always write PLL_CTL thus avoiding Anomaly 05000242 */
 	bfin_write16(PLL_CTL, PLL_CTL_VAL);
 	__asm__ __volatile__("IDLE;");
 	bfin_write_PLL_DIV(CONFIG_CCLK_ACT_DIV | CONFIG_SCLK_DIV);