df: fix "df /"

also, clean up mount checks in mkfs/fsck.

function                                             old     new   delta
find_mount_point                                     243     261     +18
sha1_process_block64                                 497     510     +13
find_main                                            436     444      +8
display_speed                                         85      90      +5
df_main                                              795     793      -2
parse_command                                       1463    1460      -3
static.ignored_mounts                                  8       -      -8
mkfs_minix_main                                     2962    2937     -25
fsck_minix_main                                     3065    2970     -95
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 4/4 up/down: 44/-133)           Total: -89 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index 835beb2..6f4c547 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -986,7 +986,7 @@
 
 #ifdef HAVE_MNTENT_H
 extern int match_fstype(const struct mntent *mt, const char *fstypes) FAST_FUNC;
-extern struct mntent *find_mount_point(const char *name, const char *table) FAST_FUNC;
+extern struct mntent *find_mount_point(const char *name) FAST_FUNC;
 #endif
 extern void erase_mtab(const char * name) FAST_FUNC;
 extern unsigned int tty_baud_to_value(speed_t speed) FAST_FUNC;