m68k: mvme16x: Remove unused sink in mvme16x_cons_write()

When building with W=1:

    arch/m68k/mvme16x/config.c: In function ‘mvme16x_cons_write’:
    arch/m68k/mvme16x/config.c:211:25: warning: variable ‘sink’ set but not used [-Wunused-but-set-variable]
      211 |         volatile u_char sink;
	  |                         ^~~~

Fix this by removing the unused variable and assignment.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/22c4d1978f811d7f4495eeb269ce06304717627a.1694613528.git.geert@linux-m68k.org