Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/drivers/mtd/nand/nomadik_nand.c b/drivers/mtd/nand/nomadik_nand.c
index 8c0b693..a045a4a 100644
--- a/drivers/mtd/nand/nomadik_nand.c
+++ b/drivers/mtd/nand/nomadik_nand.c
@@ -151,7 +151,7 @@
 	nand->options = pdata->options;
 
 	/*
-	 * Scan to find existance of the device
+	 * Scan to find existence of the device
 	 */
 	if (nand_scan(&host->mtd, 1)) {
 		ret = -ENXIO;