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/cs553x_nand.c b/drivers/mtd/nand/cs553x_nand.c
index 9f1b451..71c35a0 100644
--- a/drivers/mtd/nand/cs553x_nand.c
+++ b/drivers/mtd/nand/cs553x_nand.c
@@ -241,7 +241,7 @@
 	/* Enable the following for a flash based bad block table */
 	this->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(new_mtd, 1)) {
 		err = -ENXIO;
 		goto out_ior;