[IA64] ivt.S: typo s/idirty_bit/dirty_bit/

Patch submitted by H.J. Lu
New ia64 assembler complains if the END(tag) doesn't match
the ENTRY(tag).
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/ivt.S

@@ -548,7 +548,7 @@ ENTRY(dirty_bit)
 #endif
 	mov pr=r31,-1				// restore pr
 	rfi
-END(idirty_bit)
+END(dirty_bit)
 
 	.org ia64_ivt+0x2400
 /////////////////////////////////////////////////////////////////////////////////////////