Fix misspellings of "system", "controller", "interrupt" and "necessary".

Fix the various misspellings of "system", controller", "interrupt" and
"[un]necessary".

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
diff --git a/include/asm-arm/dma-mapping.h b/include/asm-arm/dma-mapping.h
index 678134b..1eb8aac 100644
--- a/include/asm-arm/dma-mapping.h
+++ b/include/asm-arm/dma-mapping.h
@@ -401,7 +401,7 @@
  *
  * On the SA-1111, a bug limits DMA to only certain regions of RAM.
  * On the IXP425, the PCI inbound window is 64MB (256MB total RAM)
- * On some ADI engineering sytems, PCI inbound window is 32MB (12MB total RAM)
+ * On some ADI engineering systems, PCI inbound window is 32MB (12MB total RAM)
  *
  * The following are helper functions used by the dmabounce subystem
  *