syscall: fix arm build

Rename Seek to seek in asm file, was overlooked in CL 99320043.

LGTM=bradfitz, r
R=r, rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/99320044

src/pkg/syscall/asm_linux_arm.s

@@ -103,7 +103,7 @@ ok2:
 // taking the address of the return value newoffset.
 // Underlying system call is
 //	llseek(int fd, int offhi, int offlo, int64 *result, int whence)
-TEXT ·Seek(SB),NOSPLIT,$0-32
+TEXT ·seek(SB),NOSPLIT,$0-32
 	BL	runtime·entersyscall(SB)
 	MOVW	$SYS__LLSEEK, R7	// syscall entry
 	MOVW	4(SP), R0	// fd