Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index 9dd21a8..a91626d 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -766,7 +766,7 @@
 	 * miss get to this point to load the TLB.
 	 * 	r10 - TLB_TAG value
 	 * 	r11 - Linux PTE
-	 *	r12, r9 - avilable to use
+	 *	r12, r9 - available to use
 	 *	PID - loaded with proper value when we get here
 	 *	Upon exit, we reload everything and RFI.
 	 * Actually, it will fit now, but oh well.....a common place