modem-manager: update package prompt name

Rename the prompt string for consistency with the package directory
name.

Cc: Aleksander Morgado <aleksander@aleksander.es>
Cc: Carlos Santos <casantos@datacom.com.br>
Cc: Petr Vorel <petr.vorel@gmail.com>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Acked-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/modem-manager/Config.in

@@ -1,5 +1,5 @@
 config BR2_PACKAGE_MODEM_MANAGER
-	bool "modemmanager"
+	bool "modem-manager"
 	depends on BR2_USE_WCHAR # libglib2 and gnutls
 	depends on BR2_TOOLCHAIN_HAS_THREADS # dbus, libglib2
 	depends on BR2_USE_MMU # dbus