Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/arch/xtensa/include/asm/dma.h b/arch/xtensa/include/asm/dma.h
index 137ca39..bb099a3 100644
--- a/arch/xtensa/include/asm/dma.h
+++ b/arch/xtensa/include/asm/dma.h
@@ -37,7 +37,7 @@
  *	the size of the statically mapped kernel segment
  *	(XCHAL_KSEG_{CACHED,BYPASS}_SIZE), ie. 128 MB.
  *
- * NOTE: When the entire KSEG area is DMA capable, we substract
+ * NOTE: When the entire KSEG area is DMA capable, we subtract
  *	one from the max address so that the virt_to_phys() macro
  *	works correctly on the address (otherwise the address
  *	enters another area, and virt_to_phys() may not return