[PARISC] fix trivial spelling nit in asm/linkage.h

Noticed by John David Anglin.
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

include/asm-parisc/linkage.h

@@ -8,7 +8,7 @@
 
 /*
  * In parisc assembly a semicolon marks a comment while a
- * exclamation mark is used to seperate independend lines.
+ * exclamation mark is used to seperate independent lines.
  */
 #ifdef __ASSEMBLY__