drivers: fix typo in DEVTMPFS_MOUNT Kconfig help text

rootfs was missing its f.
Signed-off-by: NEmilio López <emilio@elopez.com.ar>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/base/Kconfig

@@ -49,7 +49,7 @@ config DEVTMPFS_MOUNT
 	  with the commandline parameter: devtmpfs.mount=0|1.
 	  This option does not affect initramfs based booting, here
 	  the devtmpfs filesystem always needs to be mounted manually
-	  after the roots is mounted.
+	  after the rootfs is mounted.
 	  With this option enabled, it allows to bring up a system in
 	  rescue mode with init=/bin/sh, even when the /dev directory
 	  on the rootfs is completely empty.