treewide: fix "usefull" typo

Signed-off-by: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/base/dma-contiguous.c

@@ -49,7 +49,7 @@ struct cma *dma_contiguous_default_area;
 
 /*
  * Default global CMA area size can be defined in kernel's .config.
- * This is usefull mainly for distro maintainers to create a kernel
+ * This is useful mainly for distro maintainers to create a kernel
  * that works correctly for most supported systems.
  * The size can be set in bytes or as a percentage of the total memory
  * in the system.

drivers/net/wireless/ath/ath5k/dma.c

@@ -661,7 +661,7 @@ ath5k_hw_get_isr(struct ath5k_hw *ah, enum ath5k_int *interrupt_mask)
 			ah->ah_txq_isr_txok_all |= AR5K_REG_MS(sisr1,
 						AR5K_SISR1_QCU_TXEOL);
 
-		/* Currently this is not much usefull since we treat
+		/* Currently this is not much useful since we treat
 		 * all queues the same way if we get a TXURN (update
 		 * tx trigger level) but we might need it later on*/
 		if (pisr & AR5K_ISR_TXURN)

sound/soc/codecs/alc5632.c

@@ -614,7 +614,7 @@ struct _pll_div {
 };
 
 /* Note : pll code from original alc5632 driver. Not sure of how good it is */
-/* usefull only for master mode */
+/* useful only for master mode */
 static const struct _pll_div codec_master_pll_div[] = {
 
 	{  2048000,  8192000,	0x0ea0},