zram: ZRAM_DEF_COMP should depend on ZRAM

When Compressed RAM block device support is disabled, the
CONFIG_ZRAM_DEF_COMP symbol still ends up in the generated config file:

    CONFIG_ZRAM_DEF_COMP="unset-value"

While this causes no real harm, avoid polluting the config file by
adding a dependency on ZRAM.

Link: https://lkml.kernel.org/r/64e05bad68a9bd5cc322efd114a04d25de525940.1730807319.git.geert@linux-m68k.org
Fixes: 917a59e ("zram: introduce custom comp backends API")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: geertu

drivers/block/zram/Kconfig

@@ -94,6 +94,7 @@ endchoice
 
 config ZRAM_DEF_COMP
 	string
+	depends on ZRAM
 	default "lzo-rle" if ZRAM_DEF_COMP_LZORLE
 	default "lzo" if ZRAM_DEF_COMP_LZO
 	default "lz4" if ZRAM_DEF_COMP_LZ4