mtd: gen_probe: Use bitmap_zalloc() when applicable

'chip_map' is a bitmap. So use 'bitmap_zalloc()' to simplify code,
improve the semantic and avoid some open-coded arithmetic in allocator
arguments.

Also change the corresponding 'kfree()' into 'bitmap_free()' to keep
consistency.

Signed-off-by: Christophe JAILLET <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/a6fe58dffe[e-mail]

drivers/mtd/chips/gen_probe.c

···
 	struct cfi_private cfi;
 	struct cfi_private *retcfi;
 	unsigned long *chip_map;
-	int i, j, mapsize;
 	int max_chips;
+	int i, j;
 
 	memset(&cfi, 0, sizeof(cfi));
 
···
 		max_chips = 1;
 	}
 
-	mapsize = sizeof(long) * DIV_ROUND_UP(max_chips, BITS_PER_LONG);
-	chip_map = kzalloc(mapsize, GFP_KERNEL);
+	chip_map = bitmap_zalloc(max_chips, GFP_KERNEL);
 	if (!chip_map) {
 		kfree(cfi.cfiq);
 		return NULL;
···
 
 	if (!retcfi) {
 		kfree(cfi.cfiq);
-		kfree(chip_map);
+		bitmap_free(chip_map);
 		return NULL;
 	}
 
···
 		}
 	}
 
-	kfree(chip_map);
+	bitmap_free(chip_map);
 	return retcfi;
 }