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/pasemi_nand.c b/drivers/mtd/nand/pasemi_nand.c
index 59efa82..20bfe5f 100644
--- a/drivers/mtd/nand/pasemi_nand.c
+++ b/drivers/mtd/nand/pasemi_nand.c
@@ -157,7 +157,7 @@
 	/* Enable the following for a flash based bad block table */
 	chip->options = NAND_USE_FLASH_BBT | NAND_NO_AUTOINCR;
 
-	/* Scan to find existance of the device */
+	/* Scan to find existence of the device */
 	if (nand_scan(pasemi_nand_mtd, 1)) {
 		err = -ENXIO;
 		goto out_lpc;