Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 176f632..47f8cdb 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -74,7 +74,7 @@
 #endif
 
 /*
- * Semi-arbitary buffer size limits. 0710 is normally run with 32-64 byte
+ * Semi-arbitrary buffer size limits. 0710 is normally run with 32-64 byte
  * limits so this is plenty
  */
 #define MAX_MRU 512
@@ -82,7 +82,7 @@
 
 /*
  *	Each block of data we have queued to go out is in the form of
- *	a gsm_msg which holds everything we need in a link layer independant
+ *	a gsm_msg which holds everything we need in a link layer independent
  *	format
  */
 
@@ -1193,8 +1193,8 @@
 		break;
 		/* Optional unsupported commands */
 	case CMD_PN:	/* Parameter negotiation */
-	case CMD_RPN:	/* Remote port negotation */
-	case CMD_SNC:	/* Service negotation command */
+	case CMD_RPN:	/* Remote port negotiation */
+	case CMD_SNC:	/* Service negotiation command */
 	default:
 		/* Reply to bad commands with an NSC */
 		buf[0] = command;
@@ -2026,7 +2026,7 @@
  *	@mux: mux to free
  *
  *	Dispose of allocated resources for a dead mux. No refcounting
- *	at present so the mux must be truely dead.
+ *	at present so the mux must be truly dead.
  */
 void gsm_free_mux(struct gsm_mux *gsm)
 {