dfu:core: Find DFU alt setting number by passing its name

New function - dfu_get_alt() - has been added to dfu core. If present, it
returns alt setting's number corresponding to passed name.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
diff --git a/include/dfu.h b/include/dfu.h
index b2ecf1b..b144255 100644
--- a/include/dfu.h
+++ b/include/dfu.h
@@ -126,6 +126,7 @@
 struct dfu_entity *dfu_get_entity(int alt);
 char *dfu_extract_token(char** e, int *n);
 void dfu_trigger_reset(void);
+int dfu_get_alt(char *name);
 bool dfu_reset(void);
 int dfu_init_env_entities(char *interface, int dev);