fix seek linkage

Reference: /n/sources/patch/sorry/seeklinkage
Date: Sun Dec  7 19:08:12 CET 2008
Signed-off-by: quanstro@quanstro.net

--- /sys/src/libc/9syscall/mkfile	Sun Dec  7 19:08:09 2008
+++ /sys/src/libc/9syscall/mkfile	Sun Dec  7 19:08:08 2008
@@ -63,7 +63,7 @@
 			echo RET
 		case amd64
 			if(~ $i seek)
-				echo TEXT _seek'(SB)', 1, '$0'
+				echo TEXT seek'(SB)', 1, '$0'
 			if not
 				echo TEXT $i'(SB)', 1, '$0'
 			echo MOVQ RARG, 'a0+0(FP)'