alpha: fix objstrip.c compilation warnings

In current 2.6.23-rc1+git, make bootimage gives the following warnings while
compiling objstrip.c.  The patch below fixes these warnings by casting strncmp
argument to char * - it does not seem feasible to change its type in struct
elfhdr.

  HOSTCC  arch/alpha/boot/tools/objstrip
arch/alpha/boot/tools/objstrip.c: In function 'main':
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of 'strlen' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of 'strlen' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of '__builtin_strcmp' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of 'strlen' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of '__builtin_strcmp' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of '__builtin_strcmp' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of '__builtin_strcmp' differ in signedness
arch/alpha/boot/tools/objstrip.c:147: warning: pointer targets in passing argument 1 of 'strncmp' differ in signedness

Signed-off-by: Meelis Roos <mroos@linux.ee>
Cc: Jay Estabrook <jay.estabrook@hp.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>